mobile retro guidance presentation v12

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Contact Information:Adam Pike, P.E.Texas A&M Transportation Institute979‐317‐2136 a‐[email protected]

https://groups.tti.tamu.edu/visibility/programs-and-guidance/

Contact Information:John Bassett

Materials and Tests Division—TxDOT512‐506‐5881 [email protected]

This presentation is designed to provide information relating to the retroreflectivity requirements for TxDOT Item 666—Retroreflectorized Pavement Markings. This presentation is focused on mobile retroreflectometer measurements. Material in the presentation will help answer the following questions: What do the specifications call for? What are the providers required to do? What do the required data look like? How should the data from the providers be used?A provider is a specific contractor or subcontractor who is taking the mobile retroreflectivity measurements on a pavement marking job.

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Guidance Outline

Part 1: Introduction (5 minutes)

• Objectives

• Background

Part 2: Pavement Marking Specifications Concerning

Mobile Retroreflectivity (20‐25 minutes)

• Item 666

• Special Specification 6291

Part 3: Mobile Retroreflectivity Programs (20–25 minutes)

• Mobile Retroreflectivity Certification

• Mobile Retroreflectivity Verification

The presentation is broken down into six parts. Each part is a stand‐alone topic, but information is shared across the different parts. Some parts of the guidance summarize information to reduce duplication of material, whereas other parts go into more detail on the same information. Where information is summarized, the part of the guidance that goes into more detail is referenced.

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Part 4: Pavement Marking Retroreflectivity Equipment (25–30 minutes)• Portable Retroreflectometers

• Mobile Retroreflectometers

Part 5: Retroreflectivity Data Requirements and Analysis (35–40 minutes)• Specification Requirements

• Data Analysis

• Data Interpretation

• Comparison to Requirements

• Common Issues

• Next Steps

Part 6: Questions and Comments (<5 minutes)• TTI Mobile Retroreflectivity Website

• FAQs

• Contact Information

Guidance Outline

Some information on specification requirements from Part 2 is included in Part 5.

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Part 1:Introduction

(5 minutes)

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Introduction Outline

• Objectives

• Background

• Retroreflectivity

• Retroreflectivity Evaluations

• Specifications

• Item 666—Retroreflectorized Pavement Markings

• SS 6291—Mobile Retroreflectivity Data Collection for Pavement Markings

This section covers the objectives of the whole presentation, background material on marking retroreflectivity, how marking retroreflectivity is evaluated, and TxDOT specifications that cover marking retroreflectivity.

Other pavement marking special specifications such as SS6024—High Performance Pavement Markings with Retroreflectivity Requirements, SS6038—Multipolymer Pavement Markings, and SS6048—Reflectorized Pavement Markings for Seal Coat Projects, are not discussed in detail. These special specifications have similar requirements to Item 666. There may be differences in the required retroreflectivity values, the time frame when the measurements are supposed to occur, and the types of jobs to which the retroreflectivity requirements apply. Pavement marking specifications for all‐weather pavement markings also have mobile measurements for the dry portion of the retroreflectivity readings. They are handled in a similar fashion to other marking types.

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Objectives

• Increase user knowledge about pavement marking retroreflectivity requirements by providing information covering:• Pavement Marking Specifications Concerning Mobile Retroreflectivity

• Mobile Retroreflectivity Programs

• Pavement Marking Retroreflectivity Equipment

• Retroreflectivity Data Requirements and Analysis

• Provide users with contacts for additional information and support

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What Is Retroreflectivity?

• Retroreflectivity is a measure of the ability of amaterial to return light in the general direction fromwhich it came

• Coefficient of retroreflectedluminance (RL) is the mostcommonly usedmeasurement ofretroreflectance forpavement markings

• Units: millicandelas per square meter per lux (mcd/m2/lux)

Markings with higher initial retroreflectivity are generally going to last longer if properly applied. A higher retroreflectivity value will result in a marking that looks brighter at night. TxDOT has minimum initial retroreflectivity levels that must be met or exceeded. The specific levels depend on the specification being used. There are no federal requirements for initial or maintained retroreflectivity levels. The FHWA is working on establishing a minimum maintained value.

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Retroreflectivity Evaluations

• Portable Retroreflectivity

• Mobile Retroreflectivity

Portable retroreflectivity utilizes a handheld retroreflectometer that must be placed on the marking to take a measurement. Mobile retroreflectivity uses a vehicle‐mounted retroreflectometer that collects data while traveling at highway speeds. Both evaluation techniques will be described in more detail in latter parts of the guidance presentation. The equipment, data collection requirements, and reporting requirements will also be described.

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Pavement Marking Retroreflectivity Examples

325 200 300 50 115 75 100 400 800

510 200 55 100 165 140 85 230

These pavement markings were modified to provide a range of retroreflectivity levels for demonstration purposes. The increase in brightness of the markings as the retroreflectivity level increases is evident.

TxDOT Item 666 requires a white initial minimum retroreflectivity of 250 mcd/m2/lux and a yellow initial minimum retroreflectivity of 175 mcd/m2/lux.

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TxDOT Specifications

• Item 666—Retroreflectorized Pavement Markings• Type I marking retroreflectivity requirements

• Retroreflectivity measurement instructions

• Updated with Special Provision 007 in February 2018

• Special Specification 6291—Mobile Retroreflectivity Data Collection for Pavement Markings• Instructions and requirements for mobile retroreflectivity readings

• Verification and Referee testing requirements

• Approved in February 2018

Both Item 666 and Special Specification 6291 will be described in more detail in latter parts of the guidance presentation. Provider responsibilities, data collection requirements, and reporting requirements will be described. Interpretation of the data and how to compare to the minimum installation requirements will also be described.

Both Item 666 and Special Specification 6291 are currently undergoing revisions. Updates are expected in early to mid‐2020. This presentation will be updated as newer versions are approved.

This concludes the discussion of the introductory guidance material. Additional guidance material covering the parts previously described is provided in the other parts of the guidance presentation.

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Part 2:Pavement Marking Specifications

Concerning Mobile Retroreflectivity

(20–25 minutes)

This portion of the presentation covers the specifications that call for and control the mobile retroreflectivity data collection. There is a lot of text in this part of the guidance presentation since specific material in each specification is covered.

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Specifications Outline

• Item 666—Retroreflectorized Pavement Markings, Special Provision 666‐007, Approved in February 2018

• SS 6291—Mobile Retroreflectivity Data Collection for Pavement Markings, Approved in February 2018

• January 28, 2015—Memorandum requiring all non‐profile longitudinal pavement markings to meet retroreflectivity requirements

Item 666 was updated in February 2018 by Special Provision 007. The main areas of change included in the special provision related to the required retroreflectivity measurements.

Special Specification 6291 was approved to replace the previous Special Specification in February 2018. The areas of change included changes to the measurement notification and inclusion of verification and referee testing.

The memorandum distributed in 2015 was created to obtain uniformity of practice throughout the state.

Parts of these specifications will be discussed in other parts of the guidance presentation. The discussion in this part of the guidance presentation will not look at every part of the specifications, only those relevant to the discussion of mobile retroreflectivity.

It would be useful to have these documents available for reference during the presentation. Both of these specifications are undergoing review and modification. This presentation will be updated as newer versions are approved.

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Related Areas in Item 666‐007

• Section 3.1. General Requirements• When required to meet minimum retroreflectivity requirements on the plans:• Use a mobile retroreflectometer approved by the Materials and Tests Division and certified by the Texas A&M Transportation Institute Mobile Retroreflectometer Certification Program.

• Use a portable retroreflectometer that:• uses 30‐meter geometry and meets the requirements described in ASTM E1710;

• has global positioning system (GPS) coordinates with each reading;

• can record and print the GPS location and retroreflectivity reading for each location where readings are taken.

Updated specification required on all new jobs starting with May 2018 letting.

Mobile retroreflectometers need to be certified by TTI.

Portable retroreflectometers do not require certification but should be checked for calibration and accuracy. They are to be used to perform checks of the mobile retroreflectivity data and for small pavement marking jobs where retroreflectivity is required but the job size is not large enough to require mobile retroreflectivity. Both mobile and portable retroreflectometers evaluate the markings at the standard 30‐meter geometry. They just evaluate at a different scale. When both measurements are properly conducted, the results should be very similar.

Previously, the retroreflectometers were approved by the Construction Division; the specifications are being updated to reflect the change to the Materials and Tests Division (MTD).

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• Section 4.4. Retroreflectivity Requirements• Contracts totaling more than 20,000 ft. of pavementmarkings.

• All longitudinal edgeline, centerline or no passing barrier‐line, and lane line markings must meet requirements.

• Measured any time after 3 days, but not later than 10days after application.• White markings: 250 mcd/m2/lx• Yellow markings: 175 mcd/m2/lx

• Retroreflectivity requirements for Type I markings are notrequired for Contracts with less than 20,000 ft. ofpavement markings or Contracts with callout work,unless otherwise shown on the plans.

Section 4.4. was completely modified in Special Provision 007.

Bold and underline were added to call out specific areas of interest.

Markings must meet retroreflectivity requirements for all contracts with over 20,000 ft (total) of markings. Contracts with less than 20,000 ft of markings do not need to be evaluated for retroreflectivity unless shown on plans. Callout work does not have retroreflectivity requirements. Markings that do not have retroreflectivity requirements must still be retroreflective, but the retroreflectivity level is not evaluated.

The retroreflectivity values are for dry retroreflectivity. There are special specifications that have wet retroreflectivity requirements for pavement markings.

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• Section 4.5. Retroreflectivity Measurements

• Use a mobile retroreflectometer to measureretroreflectivity for Contracts totaling more than50,000 ft. of pavement markings.

• For Contracts with less than 50,000 ft. of pavementmarkings, mobile or portable retroreflectometersmay be used at the Provider’s discretion.

• Coordinate with and obtain authorization from theEngineer before starting any retroreflectivity datacollection.

Section 4.5. was completely modified in Special Provision 007.

Bold and underline were added to call out specific areas of interest.

Mobile measurements must be used for all contracts with over 50,000 ft of markings. Contracts with less than 50,000 ft of markings may be evaluated with either mobile or portable retroreflectometers. Remember that contracts with less than 20,000 ft of markings do not have retroreflectivity requirements that must be met, but the markings must still be retroreflective.

Providers are supposed to obtain authorization from the Engineer before starting any retroreflectivity data collection.

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Related Areas in Item 666‐007• Section 4.5.1. Mobile Retroreflectometer Measurements

• Provide mobile measurements averages for every 0.1 milesunless otherwise specified or approved.

• Take measurements on each section of roadway for each series of markings (i.e., edgeline, center skip line, each line of a double line, etc.) and for each direction of traffic flow. Measure each line in both directions for centerlines on two‐way roadways (i.e., measure both double solid lines in both directions and measure all center skip lines in both directions).

• Furnish measurements in compliance with Special Specification, “Mobile Retroreflectivity Data Collection for Pavement Markings”

• Inform the Engineer at least 24 hr. before taking any measurements.

Bold and were underline added to call out specific areas of interest.

All longitudinal markings must be evaluated. The typical averaging distance is 0.1 miles. The mobile retroreflectometer collects a continuous stream of data and is averaged at the user‐specified interval distance. Yellow centerline markings on two‐way roadways must be evaluated in both directions. For double yellow and broken/solid marking configurations, each marking must be evaluated separately. This means each edge line and lane line will each have a single set of data along its length. Yellow centerline data will have two sets of data, one for each direction of travel. Within these sets of data, there need to be separate sets of data for the right and left yellow markings.

Item 666 references the Special Specification “Mobile Retroreflectivity Data Collection for Pavement Markings.”

Providers must notify the engineer 24 hours prior to taking measurements. The special specification requires that TTI be notified as well (for verification testing purposes—described in Part 3 of the presentation).

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Related Areas in Item 666‐007• Section 4.5.1. Mobile Retroreflectometer Measurements, cont.

• A marking meets the retroreflectivity requirements if:• the combined average retroreflectivity measurement for a one‐mile segment meets the minimum retroreflectivity values specified, and

• no more than 30% of the retroreflectivity measurement values are below the minimum retroreflectivity requirements value within the one‐mile segment.

• The Engineer may accept failing one‐mile segments if no more than 20% of the retroreflectivity measurements within that mile segment are below the minimum retroreflectivity requirement value.

• The one‐mile segment will start from the beginning of the data collection and end after a mile worth of measurements have been taken; each subsequent mile of measurements will be a new segment. Centerlines with 2 stripes (either solid or broken) will result in 2 miles of data for each mile segment. Each centerline stripe must be tested for compliance as a stand‐alone stripe.

Analysis requirements are provided in this section of the specification. Data are to be analyzed in 1‐mile segments. The average over the mile needs to exceed the required values (250 white, 175 yellow), and no more than three of the ten 0.1‐mile segments can be below the required value.

There is an exception; an overall 1‐mile average that is below the required value may be accepted if only two, 0.1‐mile segments are failing. This is to allow some leeway for short areas where the marking has possibly worn due to increased traffic, such as access points or near turning areas. Yellow centerline markings need to meet or exceed the retroreflectivity requirements for both directions of travel.

Information on restriping failed sections is provided in the specification (not provided in this portion of the guidance presentation). Those paragraphs are described later in the presentation, Part 5, during the Next Steps discussion.

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Related Areas in Item 666‐007• Section 4.5.2. Portable Retroreflectometer Requirements

• Provide portable measurement averages for every 1.0 mileunless otherwise specified or approved.

• Take a minimum of 20 measurements for each 1‐mi. section ofroadway for each series of markings (e.g., edgeline, center skipline, each line of a double line) and direction of traffic flowwhen using a portable reflectometer. Measure each line in bothdirections for centerlines on two‐way roadways (i.e., measureboth double solid lines in both directions and measure all centerskip lines in both directions).

• The spacing between each measurement must be at least 100ft. The Engineer may decrease the mileage frequency formeasurements if the previous measurements providesatisfactory results. The Engineer may require the originalnumber of measurements if concerns arise.

Section 4.5.2. was completely modified in Special Provision 007.

Like the mobile measurements, all markings need to be evaluated. The portable measurements will result in much less data than can be gathered with a mobile unit. The portable measurements are time consuming and may require additional traffic control, unlike mobile measurements. Yellow centerline markings are again evaluated in both directions and evaluated separately. Unless the job is really small, most providers will use mobile measurements when there is an option between the two methods.

Information on restriping failed sections is provided in the specification (not provided in this portion of the guidance presentation). That information is described later in the presentation, Part 5, during the Next Steps discussion.

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• Section 4.6. Performance Period• All longitudinal markings must meet the minimum retroreflectivity requirements within the time frame specified. All markings must meet all other performance requirements of this specification for at least 30 calendar days after installation. Unless otherwise directed, remove pavement markings that fail to meet requirements, and replace at the Provider’s expense. Replace failing markings within 30 days of notification. All replacement markings must also meet all requirements of this Item for a minimum of 30 calendar days after installation.

The first sentence of Section 4.6. was modified in Special Provision 007.

The time frame for the retroreflectivity requirements is 3–10 days.

If markings fail for any reason, the reapplied markings must meet all requirements, including retroreflectivity.

This covers the information in Item 666 that pertains to the retroreflectivity evaluation of the pavement markings.

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TxDOT Special Specification 6291: Mobile Retroreflectivity Data Collection

for Pavement Markings• Item 666‐007 Section 4.5.1. Mobile Retroreflectometer

Measurements• Furnish measurements in compliance with Special Specification,

“Mobile Retroreflectivity Data Collection for PavementMarkings,” unless otherwise approved.

• Special Specification 6291 covers the following:• Equipment and Personnel• Mobile Retroreflectivity Data Collection Documentation

• Data File, Map, Video• Field Checks• Measurement Notification• Verification Testing• Referee Testing

The Special Specification “Mobile Retroreflectivity Data Collection for Pavement Markings” is called out in Item 666.

The special specification covers the data collection requirements and what data are required to be submitted.

The updated special specification (6291) is required starting with May 2018 letting.

Each of the items described in the special specification will be discussed in this section.

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Special Specification 6291

• Section 2. Equipment and Personnel• 2.1. Mobile Retroreflectometer. Certified by the TTIMobile Retroreflectometer Certification Program.

• 2.3. Operating Personnel for MobileRetroreflectometer. Ensure MRDC system operatorhas a current certification from the TTI MobileRetroreflectometer Certification Program to conductMRDC with the certified mobile retroreflectometerprovided.

• List of certified providers, operators, and equipment.https://groups.tti.tamu.edu/visibility/programs-and-guidance/mobile-retro-certification/certified-providers/

MRDC = mobile retroreflectivity data collection.

Equipment and personnel must be certified by TTI.

During the certification process, TTI will check any available portable retroreflectometers for accuracy at no additional charge.

TTI maintains the list of certified providers on the mobile certification website. The website is updated when changes to the list are required. In the past, physical certificates were distributed. Physical certificates are no longer distributed. Please contact the Program Coordinator (Adam Pike) if there are questions about the status of a provider, operator, or equipment.

https://groups.tti.tamu.edu/visibility/programs-and-guidance/mobile-retro-certification/certified-providers/

Adam Pikea‐[email protected]‐317‐2136

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Special Specification 6291• Section 3. MRDC Documentation

• Document all MRDC by county and roadway or as directed by the Engineer.Submit all data to the Department and to the TTI Mobile RetroreflectometerCertification Program no later than 3 working days after the day the data iscollected. Submit all raw data collected in addition to all other data submitted.Provide data files in Microsoft Excel format or a format approved by theEngineer. Provide a high‐quality DVD showing the markings as they aremeasured.

• 3.1. Preliminary Documentation Sample. Submit a sample data file, video, andmap of MRDC data in the required format 10 working days prior to beginningany work. The format must meet specification and be approved by theEngineer before any work may begin.

• 3.2. Initial Documentation Review and Approval. The Department will reviewdocumentation submitted for the first day of MRDC, and if it does not meetspecification requirements, will not allow further MRDC until deficiencies arecorrected. The Department will inform the Provider no later than 3 workingdays after submittal if the first day of MRDC does not meet specificationrequirements. Time charges will continue unless otherwise directed by theEngineer.

Section 3 of the special specification describes the data requirements. Parts 4 and 5 of this guidance presentation look at the data output from the systems, data the providers are required to turn in, and how to analyze the data.

It is necessary to receive the data from the provider within 3 days so that retroreflectivity values can be verified if needed. If the provider delays submitting the data, there will be a longer time span between provider‐collected data and verification/referee testing. This longer time span may result in changes to the retroreflectivity and may increase the difference between the data sets.

Section 3.1—Providers often do not submit the preliminary data, and districts are not requesting preliminary documentation. This is not a new addition to the specification. Districts should request this information to make sure the providers are going to submit data in the proper format. Not all districts request all information contained in this specification, and providers may assume they do not need to deliver it all when working with a new district.

Section 3.1—Districts need to review the initial documentation submission to make sure it fits their needs. If it does not, the provider needs to be notified as soon as possible so that they can modify the documentation as needed.

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Special Specification 6291• Section 3.3 Data File. Provide data files with the following:

• date;• district number; • county;• name of mobile retroreflectometer operator;• route number with reference markers or other reference information provided by the Engineer to indicate

the location of beginning and end data collection points on that roadway; • cardinal direction;• line type (single solid, single broken, double solid, etc.);• line color;• file name corresponding to video;• data for each centerline listed separately;• average reading taken for each 0.1‐mi. interval (or interval designated by the Engineer);• accurate GPS coordinates (within 20 ft.) for each interval;• color‐coding for each interval indicating passing or failing, unless otherwise directed by the Engineer

(passing and failing thresholds provided by the Engineer); • graphical representation of the MRDC (y‐axis showing retroreflectivity and x‐axis showing intervals)

corresponding with each data file; • distance in miles driven while measuring the pavement markings;• event codes (pre‐approved by the Engineer) indicating problems with measurement;• portable retroreflectometer field check average reading and corresponding mobile average reading for that

interval when applicable; and • upper validation threshold (may be included separately with the raw data but must be clearly identified with

the data collected using that threshold).

Each of these items should be provided on the summary data file. Examples of data files are provided in Parts 4 and 5 of this guidance presentation.

Providers format their data files in different ways. There is not a standard format that providers must follow. The files should contain the information listed unless not required by the district.

There are some differences between mobile retroreflectometers, their software, and their output data that may affect some of the above required items. These differences are described in Parts 4 and 5 of the presentation.

As noted in Section 3 of the special specification, the raw data should be submitted in addition to the required summary data as described in Section 3.3. The summary data provide a good overview of the information collected and if the markings pass or fail the retroreflectivity requirements. Looking at the summary data, an observer can sometimes judge the quality of the data. If the accuracy of the data looks questionable, the raw data can be reviewed to see if there may be some issues with the data.

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Special Specification 6291• Section 3.4. Map. Provide a map in an electronicformat approved by the Engineer with each MRDCsubmission that includes the following information:• date;• district number;• county;• color‐coded 1‐mi. intervals (or interval length designatedby the Engineer) for passing and failing retroreflectivityvalues or retroreflectivity threshold values provided by theEngineer; and

• percentage of passing and failing intervals, if required bythe Engineer.

Each of these items should be provided on the map file. Examples of map files are provided in Parts 4 and 5 of this guidance presentation.

Providers format their map files in different ways. There is not a standard format that providers must follow. The files should contain the information listed unless not required by the district.

There are some differences between mobile retroreflectometers, their software, and their output data that may affect some of the above required items. Most of the providers are submitting map files generated directly by the software provided with their mobile retroreflectometer. There is not much room to change these files. TTI has worked with the equipment manufacture’s to try to get the data in alignment with the specifications. Most map files have the data color‐coded by the length of the data acquisition interval (i.e. typically 0.1‐mile segments). Percent intervals passing or failing is not necessarily needed on the map files, since it is part of the data file. Google Earth files should be requested from the providers.

The map files are useful to get a visual representation of the retroreflectivity values along the length of the section. Multiple files can be combined and layered to show a broader overview of the retroreflectivity quality of the markings. Using a satellite image can help identify why there may be drops in retroreflectivity along certain parts of a roadway (access points/turning movements).

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Special Specification 6291• Section 3.5. Video. Provide a high‐quality DVD with the following

information:• date and corresponding data file name on label;• district number;• county;• route number with reference markers or other designated reference

information to indicate the location of beginning and end collection points onthat roadway; and

• retroreflectivity values presented on the same screen with the followinginformation:• date; • location;• starting and ending mileage; • total miles;• retroreflectivity readings; and• upper validation thresholds (may be included separately with the raw data but must be

clearly identified with the data collected using that threshold).

Each of these items should be provided on the video file. The specification indicates a DVD, but electronic files are preferred. A pending update to the special specification has modified this to indicate an electronic file. The new equipment provides electronic files that are simple to transfer and of good video quality. Examples of video files are provided in Parts 4 and 5 of this guidance presentation.

Providers format their video files in different ways. There is not a standard format that providers must follow. The files should contain the information listed unless not required by the district.

There are some differences between mobile retroreflectometers, their software, and their output data that may affect some of the above required items. Most of the providers are submitting video files generated directly by the software provided with their mobile retroreflectometer. There is not much room to change these files. TTI has worked with the equipment manufacture’s to try to get the data in alignment with the specifications.

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Special Specification 6291• Section 3.6. Field Comparison Checks with a Portable Retroreflectometer.

• Take a set of field comparison readings with the portable retroreflectometer atleast once every 4 hours while conducting MRDC or at the frequency designatedby the Engineer. Take a minimum of 20 readings, spread out over the interval measured. List the average portable retroreflectometer reading next to themobile average reading for that interval with the reported MRDC data. Requestapproval from the Engineer to take field comparison readings on a separateroadway, when measuring a roadway where portable retroreflectometer readingsare difficult to take. Take the off‐location field comparison readings at no additionalcost. Submit the portable retroreflectometer printout of all the readings taken forthe field comparison check with the corresponding MRDC data submitted. Themobile average reading must be within ±15% of the portable average reading. TheEngineer may require new MRDC for some or all of the pavement markingsmeasured in a 4‐hour interval prior to a field comparison check not meeting the±15% range. Provide the new MRDC at no extra cost to the Department. TheEngineer may take readings with a Department portable retroreflectometer to ensure accuracy at any time. The Department’s Materials and Tests Division (MTD)will take comparison readings and serve as the referee if there is a significantdifference between the Engineer’s portable readings and the Provider's mobile andhandheld readings. For best results, take field comparison readings on a fairly flatand straight roadway when possible.

Most providers are not submitting these field comparison checks, and most districts are not requesting these measurements be taken. This is not a new addition to the specification.

Periodic comparison of the mobile data to a portable system will help ensure accurate readings are being collected. Providers do not want to do this because it takes time and is a safety issue. Safety is important, and these portable readings should not be requested on high‐volume roads. Early in a contract, an unfamiliar provider, or past experience, should dictate the rate at which portable comparisons are required/requested. The district should try to check readings as often as possible to make sure accurate data are being collected until they are comfortable with the provider. Spot retroreflectivity readings can help give an idea as to the quality of the marking for quality assurance purposes.

Twenty readings over a tenth of a mile section is a sufficient number to be confident in the average value collected. Twenty readings will provide more than 95% confidence that the average value is within one half of a standard deviation of the data set. i.e. if the 20 readings average 350 with a standard deviation of 40, you can be 95% confident that the average value is 350 ± 20.

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Special Specification 6291• Section 3.7. Periodic Field Checks at Pre‐MeasuredLocations.• When requested by the Engineer, measure with the mobileunit and report to the Engineer immediately aftermeasurement the average retroreflectivity values for adesignated pre‐measured test location. The Engineer willhave taken measurements at the test location within 10days of the test. The test location will not includepavement markings less than 30 days old. If the measuredaverages do not fall within ±15% of the pre‐measuredaverages, further calibration and comparisonmeasurements may be required before any further MRDC.Submit the results of the field check with the MRDC reportfor that day.

This is an old method some districts had used to make sure operators were collecting accurate retroreflectivity data. It is a good method but requires effort from the district to establish these comparison test areas. It also requires the provider to possibly go out of its way to evaluate these specific field check locations.This type of field check is more useful when a provider is reading many roads in a relatively small area (i.e., seal coat striping, restriping, or maintenance‐level readings).

This type of field check may be useful for new providers or providers who have previously submitted questionable or inaccurate data.

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• Section 3.8. Measurement Notification.

• Provide notification via email [email protected] a minimum of 24 hoursprior to mobile retroreflectivity data collection toallow for scheduling verification testing whenneeded.

Item 666 requires that the engineer be notified at least 24 hours in advance; Special Specification 6291 requires that TTI be notified as well. Notification of TTI is a new addition to the specification. TTI needs to be notified for all projects.Districts are also welcome to notify TTI if they are having issues or would like a provider checked.

From TTI’s perspective, it would be ideal if providers submitted weekly work plans on Monday instead of daily plans every day. This weekly work plan would indicate which roads they are planning to read, what job those readings are part of, and when those roads were striped. There is an understanding that these plans may change some due to delays or weather. The 3–10 day window still needs to be met; any delays beyond that are on the provider and cannot be used as an excuse for failing readings.

Many providers are currently providing adequate notification to TTI, but some are not. Those who do not provide adequate notification will be removed from the certified providers list until they come into compliance with the notification requirements.

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Special Specification 6291• Section 3.9. Verification Testing.

• The Engineer or a third party may perform retroreflectivity verification testing within 7 days of the Provider’s retroreflectivity readings. The Provider‐submitted retroreflectivity data will be compared to the verification test data to determine acceptability of the Provider’s mobile retroreflectometer data. Comparison of the data will result in one of the two scenarios below: • Provider’s Data is Validated – If the difference between provider’s and

Engineer/third party data is 20% or less, then the provider’s data is validated. The provider’s data will be used for acceptance.

• Provider’s Data is not Validated – If the difference between provider’s and Engineer/third party data is more than 20%, then the provider’s data is not validated. The Engineer/third party data will be used for acceptance and the provider will be required to take corrective action prior to additional provider data collection and may require re‐certification of the mobile retroreflectometer. If the Engineer determines that the provider’s data might be correct then, Referee Testing may be requested by the Engineer.

TTI or the district can perform verification testing on the provider. The TTI verification testing program will be described in Part 3 of this guidance presentation.

The goal of the verification testing is to collect an accurate set of data in as close a time frame as possible to when the provider collected its data. These two data sets are compared to check the quality of the provider's data.

Providers whose data are less than 20% different from the verification data will be notified of the validated results.

Providers whose data exceed 20% difference from the verification data set will be provided with the results and information concerning corrective actions to improve future data collection. Repeated non‐validation of data will result in loss of certification, described in Part 3 of this presentation.

If the data are not verified and both data sets indicate data that exceed the minimum retroreflectivity requirements, then the engineer can accept the job. If there is conflict between the data sets, where one indicates passing markings and the other does not, the engineer can request referee testing.

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• Section 3.10. Referee Testing.

• MTD will perform referee testing using portableretroreflectometers to determine if the markingsneed to be restriped to meet the requiredretroreflectivity level. The referee test results willbe final. Referee testing will be conducted on theverification test section(s) using the method forportable retroreflectometers specified in Item 666,“Reflectorized Pavement Markings.”

TxDOT MTD will perform the referee testing. Referee testing should occur as soon as possible after conflicting measurements are found and cannot be resolved. Delays in performing referee testing may result in data that are not as easy to compare due to the impact of time on the degradation of marking retroreflectivity.

Referee testing can occur with or without TTI verification testing. If the district checks the provider’s work and the provider disputes the results, referee testing can be conducted to resolve the dispute.

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• Section 4. FINAL REPORT

• Submit a final report in the format specified bythe Engineer to the Department’s TrafficEngineering representative within 1 calendarweek after the service is complete. The finalreport must contain a list of all problemsencountered (pre‐approved event codes) and thelocations where problems occurred during MRDC.

If a final report is to be submitted, it must be submitted within 1 week after the service is complete.

The final report is in addition to the individual data (Excel, map, video) submissions. TTI is not aware of final reports being regularly submitted by the providers or the frequency of use by TxDOT.

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Summary

• Pavement Marking Specifications ConcerningMobile Retroreflectivity

• Item 666


The pavement marking retroreflectivity requirements, especially the mobile retroreflectivity requirements, from these two specifications were described. Each specification outlines certain criteria and requirements that need to be followed. The providers and TxDOT need to understand and follow the specifications to make sure markings are meeting the minimum initial retroreflectivity requirements.

This concludes the discussion of the specifications concerning mobile pavement marking retroreflectivity.

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Part 3:Mobile Retroreflectivity Programs

(20–25 minutes)

This portion of the presentation covers the mobile retroreflectivity programs that are listed and required in Item 666 and the Special Specification “Mobile Retroreflectivity Data Collection for Pavement Markings.” TTI manages both of these programs and reports to TxDOT Materials and Tests Division (MTD).

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Mobile Retroreflectivity Programs Outline

• Mobile Retroreflectivity Certification• Overview• Requirements• Certified Providers/Equipment

• Mobile Retroreflectivity Verification• Overview• Responsibilities

• TTI• TxDOT• Provider

• Results• Maintaining Certification

The two programs are the mobile retroreflectivity certification program and the mobile retroreflectivity verification program. The certification process is necessary to make sure the operators and equipment have the ability to collect accurate data and submit those data in compliance with TxDOT specifications. The certification program does not guarantee the providers will collect accurate data in the field. The certification program is for new providers, new operators, new equipment, and providers who have lost certification.

The verification program is being used to evaluate field performance of the providers on TxDOT jobs. Observations and inspection by TxDOT are also necessary to make sure providers are collecting accurate data.

TTI conducts both the certification and verification programs.

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Certification Program Background

• Certification program started in Spring 2007

• Program was developed after TxDOT questioned the validity of mobile retroreflectivity data submitted as part of a contract

• The data were highly variable and didn’t always make sense

• TxDOT questioned the ability of the provider to operate the equipment and wanted providers to be tested to make sure they have the ability to collect accurate data

TxDOT and TTI worked together to develop the program, which TTI manages.

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Certification Program Overview

• Prior to conducting work for TxDOT, providers mustcome to TTI and pass the certification test

• Certification testing is required for all new operatorsand equipment

• There is a fee associated with the certification test

• In the past, certification was maintained throughannual recertification

• Certification is now maintained through the fieldverification program

• Loss of certification due to poor retroreflectivityverification results requires full recertification testing

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• Closed‐course and open‐road testing

• All line types and colors measured

• Certification program guide detailsinformation about the program

• Certification guide and other information canbe found on the certification website:


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Closed‐course test area at the Texas A&M University System RELLIS Campus.

Markings cover a range of retroreflectivity levels and marking material types.

Paint, thermoplastic, structured thermoplastic, epoxy, and tape are included oncertification course.

Open‐road tests include thermoplastic and paint pavement markings.

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Certification Testing Requirements

• Mobile retroreflectivity data must be within±15% of the portable retroreflectivity valuecollected on the same pavement markingsegments

• Data are evaluated for each individual run andfor the test as a whole

• Contactors must submit examples of data, map,and video files that meet specificationrequirements

Comparison portable measurements are taken frequently on the test marking, at 20–40 foot spacing. These measurements are typically within 1 day of the certification test.

The provider mobile retroreflectivity data are compared to the TTI portable retroreflectivity data. TTI also evaluates the markings with its mobile retroreflectometer and incorporates those data into the comparison as well.

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Number of Certified Providers

• Five different mobile retroreflectometer types have beencertified

4 4

6 67

9

11 11

14

1918 18 18

0

2

4

6

8

10

12

14

16

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2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019

Number of Certified Providers

Year

There are currently four different mobile retroreflectometer types certified. One of the previously certified retroreflectometer types is no longer certified.

The total number of providers certified fluctuates some if providers lose certification or if out‐of‐state providers do not maintain certification.

The jump in providers in 2015 and 2016 is likely due to the TxDOT mandate on initial retroreflectivity requirements for most new markings that was released in early 2015.

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List of Certified Providers/Operators and Equipment

• List can be accessed on the certification programwebsite

• List is regularly updated as new operators orequipment certify, or if a provider losescertification


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Mobile Retroreflectivity Verification Program

• Federal regulations require DOTs to verify provider testresults for performance‐based product acceptance

• Guideline is to perform verification on a minimum of10% of projects

• TTI is working with TxDOT to meet these requirements• Verification or spot monitoring can also be conducted bydistricts contracting the work to ensure accurate data areconsistently collected

https://groups.tti.tamu.edu/visibility/programs-and-guidance/retroreflectivity-verification-program/

Most longitudinal markings have retroreflectivity requirements that need to be met for project acceptance.

Verification testing was added to Special Specification 6291.

TTI is conducting a formal verification testing program. TxDOT districts still need to monitor the providers at some level to make sure they are following the specifications, installing quality markings, and providing accurate data.


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TTI Responsibilities

• Manage verification program

• Coordinate field verification evaluations

• Analyze data from field evaluations

• Report to provider and TxDOT on field verificationevaluation results• Each job included in verification program

• Monthly reports to MTD

• Annual report to MTD

• Recommend changes to the program asnecessary

These are the major responsibilities for TTI. Each will be discussed in more detail on the following slides.

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Verification Program Management

TTI is:

• Using a SiteManager materials report to monitor and assist in project selection

• Initially selecting 20% of projects, with a goal of evaluating 15% to ensure the 10% requirement is met

• Coordinating field evaluation and reporting results

• Notifying providers of program changes

TxDOT has provided TTI with access to SiteManager to access project information for projects that include Item 666. This allows TTI to identify projects and monitor when and how many projects have been let.

The goal is to select more projects than needed because ultimately all of them will not be evaluated. Things like weather, bad data, construction delays, issues with the provider, unavailability, etc. may prevent specific projects from being evaluated in a timely manner as compared to when the provider evaluates the markings.

Part of the management of the program is coordinating the field evaluations and reporting the results; those areas will be described later in this section.

TTI, in cooperation with TxDOT, will notify the providers of changes to the program or changes to specifications.

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Coordinate Verification Evaluations• Providers notify TTI of measurements

• TTI verification data are collected within 7days of provider data

• TTI schedules readings to get a representativedistribution around the state and amongproviders

• Providers will not know which projects TTI hasselected for verification testing

Providers are required to notify TTI at least 24 hours in advance of conducting mobile retro readings. TTI hopes providers will send a weekly plan on Monday of what they anticipate reading during the week. This will allow TTI to better plan data collection and will result in TTI collecting data closer to when the providers collect their data.

TTI data need to be collected in the nearest time frame possible to the provider to minimize potential differences in the data due to outside factors such as weather, traffic, dirt, etc. TTI will try to collect data within 3 days of the provider.

Providers will be evaluated multiple times per year. If providers have had issues with readings, they will be evaluated more frequently to make sure their readings are meeting the accuracy requirements. For example, TTI evaluates a provider who has had accurate data in the past but whose most recent evaluation is well outside the accuracy requirements. TTI will look to evaluate the provider again in a short time frame to see if it has implemented corrective action (described later) or if it possibly has equipment issues that will require it to have its equipment serviced. Loss of certification based on verification results will be described later.

In previous years, scheduling required TTI to contact the providers to determine when and where they were taking measurements. The providers could assume if TTI was contacting them that TTI was going to evaluate those jobs. With the changes to Special Specification 6291, the providers now need to notify TTI of all measurements they will be taking, so they will not know which jobs have been selected for verification testing.

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Analyze Data

• Provider mobile data are compared to TTI mobile data (supplemented with portable readings for accuracy verification)

• Data must differ by 20% or less to meet verification accuracy requirements• Data between 20% and 35% = 1 strike• Data exceeding 35% difference = 2 strikes

• TTI will also check to see if the data meet the minimum retroreflectivity requirements

TTI regularly maintains its mobile and portable retroreflectometers and constantly tests them to ensure accurate data are collected. Mobile measurements are supplemented with portable measurements to verify accuracy.

Provider collected data must be within 20% of the TTI data to meet the verification accuracy requirements. If the data differ between 20 and 35%, the provider will get a strike, and if the data differ by more than 35%, the provider gets two strikes. Three consecutive strikes will result in the provider losing certification and needing to go through the certification process again in order to be able to collect data on TxDOT projects. The provider will lose a strike (if it has one) if the provider’s data meet the verification accuracy requirements.

TTI will check if the data meet the Item 666 minimum initial retroreflectivity requirements, 250 for white and 175 for yellow.

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Reporting Results

• Individual jobs are reported to the providerand district• Did provider meet verification requirements?

• Did markings meet retroreflectivity requirements?

• TTI submits monthly reports to MTDdocumenting verification evaluations

• TTI submits annual report to MTDdocumenting all work completed and programstatus

In the past, results have only been going to the providers and MTD. The results were not sent to the district unless requested. Results will be sent to the districts in the future.

TTI will continue to update MTD on a monthly and annual basis. As needed, meetings will also be held to discuss the status of the program and any changes that would be beneficial.

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Annual Program Review

• Annual report will include a section reviewing the program• How are the providers doing?

• Accuracy of readings• Quality of markings

• Are the accuracy requirements set to an appropriate level?

• Are changes needed for notifications, reporting, or corrective action requirements?

• Recommend changes to the program will be made as necessary

With each annual report, TTI will describe the work conducted, the results, and if any changes should occur to improve the program.

Feedback collected throughout the year from providers, districts, and MTD will be considered when making recommendations on changes to the program.

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TxDOT Responsibilities

• Support verification program

• Conduct referee testing (MTD)

• Contact TTI for specific jobs to evaluate

• Ensure providers are certified

• Make sure providers are following the specifications

• Hold providers accountable

These are district or area office level responsibilities, except for the first two bullets. The last four bullets are TxDOT responsibilities that apply to all pavement marking jobs, not just those included in the verification program. The districts need to monitor all pavement marking projects, make sure contractors submit the appropriate data, and review the data to make sure they meet requirements. TTI is only evaluating contractor data for a portion of the projects across the state.

TxDOT can contact TTI to evaluate specific projects if desired.

TxDOT needs to go to the certification website to make sure the providers that are performing work are certified. TxDOT can contact TTI directly if they have any questions about certification status.

TxDOT should make it clear in the contract if it desires any specific changes to the specifications. Things such as data formatting or what data to collect and submit may be desirable to change. Providers need to turn in sample data to prove they can supply the specified data. Providers must also notify TxDOT about upcoming measurements.

Providers need to be held accountable. They need to collect and turn in data on time. If they delay in collecting the data, the minimum requirements should not be relaxed. If markings are below minimum retroreflectivity requirements, they need to be restriped. If providers are not providing the data that they should be, and the data are wanted, then they need to provide those data at no additional cost.

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Referee Testing

• The Engineer can request referee testing if thedata do not validate and results are conflictingfor meeting minimum retroreflectivityrequirements

• MTD will perform the referee testing usingportable retroreflectometers

• Referee testing will be conducted according toItem 666 portable retroreflectometermeasurements

Referee testing needs to be requested as soon as possible. The influence of other factors (traffic, weather, etc.) will have a greater impact the longer the time is between the first set of collected data and the referee testing. If the time frame is too long, the referee data may differ solely because of these other factors and may not reflect the quality of the pavement markings during the 3–10 day window when initial retroreflectivity is supposed to be evaluated. That being said, if a marking loses a large portion of its retroreflectivity in a short time frame, then the marking was likely not very good to begin with.

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Provider Responsibilities

• Meet contract and specification requirements• Provide sample data• Receive authorization for retroreflectivity measurements from engineer

• Notify TxDOT and TTI at least 24 hours prior to mobile measurements

• Submit data to TxDOT and TTI• Maintain equipment and certification status• Certification• Accurate field verification evaluations• Perform corrective actions when necessary

Providers need to meet the requirements of the TxDOT specifications. These requirements include:• Providing sample data for TxDOT to review.• Not starting retroreflectivity readings until given authorization from the TxDOT Engineer.• Providing notification to TxDOT and TTI at least 24 hours prior to collecting

retroreflectivity data on any individual job.• Submitting the collected, summarized, and properly formatted data to TxDOT and TTI.

Providers must maintain their equipment so that it can collect accurate data.

Providers must also maintain certification of their equipment and operators. Initial certification can be obtained through the TTI certification program. Maintaining certification occurs through collecting accurate field data as part of the verification program.

If necessary, providers must perform corrective actions in the event that field verification data do not meet accuracy requirements. These actions will be provided by TTI when the verification results are provided.

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Provider Corrective Actions

• Corrective actions need to take place or elsecertification status can be lost after multiplefailed verification tests

• Recommended corrective actions will beprovided to the provider with the results

• Possible corrective actions• Have equipment serviced

• Improve calibration procedure and frequency

• Adjust software settings

• Monitor data collection conditions

These are examples of corrective actions. Specific actions, such as the specific software setting to adjust or monitor, will be provided on a case‐by‐case basis. Corrective actions need to take place to improve accuracy of collected retroreflectivity data to reduce the chances of failing future verification evaluations.

Some data differences may be caused by the environment and will be noted in the results. Seal coat roadways are typically more difficult to stripe with a new marking than other road surfaces due to the profile of the road surface. It is especially difficult to stripe a yellow centerline because the opposite direction of application often gets fewer beads due to the forward motion of the striping and the profile of the aggregate. Seal coat roadways may bleed asphalt that can get tracked on the markings. This is typically not the fault of the striping company and needs to be accounted for when conducting verification readings, reporting on the results, and holding the providers accountable.

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Verification Results

• TTI will check two things:1. Do the provider data fall within ±20% of the TTI data?

2. Do the provider and/or TTI data meet theretroreflectivity requirements?

• Item 1 is for the verification program; TTI will takeaction on failing data.

• Item 2 is additional comparison provided to TxDOTto make sure the markings are meetingspecifications; TxDOT will need to take action onfailing or questionable data.

In the TTI responsibilities section, the data analysis and reporting of the results were discussed.

This section provides additional details as to what is being compared and how the results are to be used.

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Notification of Results• TTI will provide the results to the TxDOT engineer incharge of the project as well as the provider

• Possible results:• Data are verified and are above requirements (good)• Data are verified but are below requirements (restripe)• Data are verified but are above/below requirements (refereetest?)

• Data are not verified but are above requirements (correctiveactions)

• Data are not verified and are below requirements (restripe,corrective actions)

• Data are not verified and are above/below requirements (refereetest? corrective actions)

TTI will notify both the provider and the TxDOT engineer in charge of the project. It is impossible for TTI to know the correct contact for each project since districts handle striping differently. Even within districts, maintenance or construction striping is often handled differently. TTI will send the results to the person noted as the project contact. It is expected that that person, if they are not the correct person, will send the information on to the correct person. Over time, as contact is made with each district, a list of appropriate contact persons will be developed if there are specific people at the districts who deal with striping or the retroreflectivity data.

There are six basic scenarios of the results. Only one of them is good for both the verification testing and meeting the minimum retroreflectivity requirements. The other five are a combination of passed and failed verification with passed, failed, or inconclusive on meeting the minimum retroreflectivity requirements. When the data are inconclusive on meeting the minimum retroreflectivity requirements, referee testing may be necessary.

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Sample Results Notification

This is an image of a sample results notification form. The design and content on the form may change as feedback is received from districts.

General information on the project evaluated will be provided with the results.

Summary information on the results will be provided on a line‐by‐line basis as well as for the whole project.

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Sample Results Notification

In addition to general information on the project evaluated, the data collected may also be displayed. This slide has two different methods of displaying the data.

The top chart is a way to show the distribution of the data collected over the entire length of the pavement marking in a simple box and whisker plot. It shows the average and the distribution of the data. These plots can be used to show the differences between the TTI and provider data. This method of displaying the data is more useful for the verification program because it is more concise it does not show how the retroreflectivity changes along the length of the line, just the aggregated data over the entire length.

The bottom chart is more useful for determining if the data pass minimum retroreflectivity requirements or not. The data indicated in the graph are from a white edge line that passed verification. There was an 8.5% difference between the TTI and provider data. On average, the provider data were about 30 mcd/m2/lux higher than the TTI data over the length of the project. There were only a couple of short areas where the retro value fell below the minimum requirements. The specific data outputs would need to be evaluated to determine if restripe was needed. This will be discussed in Part 5 of the presentation, which focuses on the data requirements and how to analyze the data.

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Maintaining Certification

• Continued accurate field verifications

• Data must differ by 20% or less to meetverification accuracy requirements• Data between 20% and 35% = 1 strike• Data exceeding 35% difference = 2 strikes

• Three strikes result in the loss of providercertification, and require full recertification atTTI

• Passed verification results in loss of a strike

Provider‐collected data must be within 20% of the TTI data to meet the verification accuracy requirements. If the data differ between 20 and 35%, the provider will get a strike, and if the data differ by more than 35%, the provider gets two strikes. Three consecutive strikes result in the provider losing certification and needing to go through the certification process again in order to be able to collect data on TxDOT projects. The provider will lose a strike (if has one) if the provider’s data meet the verification accuracy requirements.

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Summary

• Mobile Retroreflectivity Programs

• Mobile Retroreflectivity Certification

• Mobile Retroreflectivity Verification

The certification and verification programs serve two separate but related purposes. The providers need to meet the requirements of both programs, and TxDOT needs to hold them accountable. TTI has to rely on input from the providers and TxDOT. If the providers are not following the program rules, then TxDOT needs to notify TTI and hold the provider accountable. If providers are not held accountable, it will hurt the quality of markings being applied and creates an inequitable contracting environment in which different providers may be held to different standards by different districts.

This concludes the discussion of the certification and verification programs.

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Part 4:Pavement Marking

Retroreflectivity Equipment

(25–30 minutes)

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Pavement Marking Retroreflectivity Equipment Outline

• Portable Retroreflectometers• Calibration• Operation• Requirements• Data Output

• MobileRetroreflectometers• Calibration• Operation• Requirements• Data Output

Some of these topics are covered in more detail in other parts of the guidance presentation.

The specification requirements are covered in more detail in Part 2.

The data output is briefly described in this part of the presentation and is described in more detail in Part 5 when discussing the analysis of the data.

Portable retroreflectometers are often called handheld retroreflectometers.

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Portable Retroreflectometers

• Simple to use, accurate data

• Must be placed directly on the marking

• Limited amount of data can be collected

Portable retroreflectometers are simple to calibrate and operate. It does not take much training to operate them properly.

Portable retroreflectometers must be placed directly on the marking and left there for a few seconds while a measurement is taken. They do need to be placed on a flat surface, if the instrument is not level or is wobbly, the accuracy of the data may not be good.

Having to place the retroreflectometer directly on the marking results in a slow process that exposes the user to traffic. The slow process means a good data collection plan must be used to get a representative sample of the marking. Item 666 Section 4.5.2., Portable Retroreflectometer Requirements, describes the quantity of data to be collected. It will be discussed in a few slides.

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Portable Retroreflectometer Calibration

• Calibration should be performed regularly

• A calibration block is placed on theretroreflectometer

• A calibration reading is taken

• The retroreflectometer is ready to use

A full calibration or a check of the calibration should take place daily. A full calibration goes through the full calibration process. A calibration check just evaluates the calibration blockto make sure it is reading the correct value.

The calibration block is placed on the retroreflectometer, and the calibration block value is entered into the retroreflectometer.

The calibration readings are taken and the unit is then ready to use.

Calibration should follow the manufacturer’s recommended process.

Calibration blocks need to be taken care of so they do not get dirty. A dirty calibration block will affect the accuracy of the calibration and thus the accuracy of the readings.

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Portable Retroreflectometer Operation

• Make sure measurement window is clean

• Calibrate or check calibration

• Place retroreflectometer on marking• Should sit level

• Should be on a representative location

• Should not be placed too close to the start or end of a line

• Should be centered on the marking across its width

• Press button to take reading

• Wait until measurement is complete

• Move to next location

These steps outline the general process for conducting portable retroreflectivity measurements of pavement markings. The operator needs to make sure the unit’s GPS is activated and properly working prior to taking readings.

It is important that the retroreflectometer is placed so that the measurement area is completely over the pavement marking. Keep in mind that most portable retroreflectometers read an area about 2 inches wide and about 8 inches long, at a location out in front of the retroreflectometer. Generally, the retroreflectometer should be centered across the marking width, and placed at least a foot away from any end of a marking. This location needs to be representative of the marking as a whole (i.e., do not place on a spot covered with dirt when the rest of the marking is clean). The retroreflectometer should sit relatively level and not rock back and forth or side to side. Once the retroreflectometer is in position a measurement takes only a second or two. Measurements need to be taken in the direction that the markings will be observed by drivers.

If different line types are being evaluated, then different file names should be set up in the equipment to separate the readings so that there is no confusion as to which lines or direction of travel the readings belong to.

Rumble stripe markings and profile markings are difficult to evaluate with a portable retroreflectometer. Additional readings are required to get an accurate average value. The equipment needs to be modified or held in a level position while taking the readings so that the geometry of the measurement is correct. The portable retroreflectometer should

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not sit in the bottom of the depressions; it should be positioned so that it lays flat across the top of the marking.

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Portable Retroreflectometer Specification Requirements

• Measurements using a portable retroreflectometer are an option for contracts totaling between 20,000 and 50,000 ft. of pavement markings.

• Markings must be evaluated after 3 days but not later than 10 days after application.

• Retroreflectivity requirements are the same as for mobile measurements (250—white, 175—yellow)

Additional and more detailed information is provided in Part 2 of the guidance presentation, Pavement Marking Specifications Concerning Mobile Retroreflectivity.

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Portable Retroreflectometer Specification Requirements

• Item 666 Section 4.5.2. Portable Retroreflectometer Requirements (summary)• Provide portable measurement averages for every 1.0 mile.

• Take a minimum of 20 measurements for each 1‐mi. section of roadway for each series of markings (e.g., edgeline, center skip line, each line of a double line) and direction of traffic flow.

• Measure each line in both directions for centerlines on two‐way roadways.

• The spacing between each measurement must be at least 100 ft.

Additional and more detailed information is provided in Part 2 of the guidance presentation, Pavement Marking Specifications Concerning Mobile Retroreflectivity.

Each individual marking should have a separate set of data collected at the required intervals. For large data sets, the equipment can be programed with file names for each line type to aid in data organization. Switching between line types on a portable retroreflectometer only takes a few button pushes and will greatly aid in processing the data later on.

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Portable Retroreflectometer Data Output

• Can be printed or downloaded

• Downloaded data are in spreadsheet format

• GPS coordinates provided with each reading

• Individual readings provided

• Running average provided, can be set to average any number of readings

• Important to not mix line types unless different file names are used

Large data sets should be downloaded electronically. The data can easily be averaged and submitted from the electronic download files.

The data output contains the GPS information, individual and average retroreflectivity readings, and line type, and can contain other user‐entered information.

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Mobile Retroreflectometers

• More complicated to use, accuracy can vary

• Data can be collected from a vehicle traveling at highway speeds

• Large amounts of

data can be collected

• Safer than portable

Mobile retroreflectometers are more complicated to set up, calibrate, and operate thanportable retroreflectometers. Each of these factors can lead to variations in the collected retroreflectivity data. It takes training and experience to properly operate a mobile retroreflectometer. The newer style mobile retroreflectometers are more accurate and easier to operate than the older style.

Mobile retroreflectometers are mounted on the side of a vehicle and collect data while traveling at highway speeds. The retroreflectometers can be mounted on fixed mounting hardware or by using vacuum mounts that allow for portability of the unit to multiple vehicles.

The mobile nature of the data collection does not expose the users to traffic other than driving in the traffic. Large amounts of data can be collected; typically the entire length of each marking of each project is evaluated.

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Mobile Retroreflectometer Calibration

• Calibration should be performed regularly

• A calibration block or calibration marking panel is placed on or in front of the retroreflectometer

• A calibration reading is taken

• The calibration value is verified

• The retroreflectometer is ready to use

A full calibration or a check of the calibration should take place every 4 hours or so, typically at startup and midday. A full calibration goes through the full calibration process. A calibration check just evaluates the calibration block to make sure it is reading the correct value.

The calibration block or pavement marking sample is placed on or in front of the retroreflectometer, and the calibration value is entered into the retroreflectometer. The calibration process is started in the software, and once complete, the unit is calibrated.

Older style mobile retroreflectometers require comparison to a short stretch of marking evaluated with a portable retroreflectometer to ensure accurate calibration. This short stretch of marking must be evaluated with a portable retroreflectometer and then evaluated with the mobile retroreflectometer at speed. If the mobile and portable readings compare well with each other, then the system is accurately calibrated. The newer style mobile retroreflectometers can be accurately calibrated and have their calibration checked by simply evaluating the calibration blocks.

After calibration, the mobile retroreflectometer will be ready for use.

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Mobile Retroreflectometer Operation

• Mount retroreflectometer on vehicle• Make sure measurement window is clean• This should be monitored frequently during data collection

• Check software settings• Calibrate or check calibration• Create file name• Evaluate the marking for the length of the project• Separate files need to be created for separate markingsand directions of travel

• Monitor software during data collection• Download data

The operation of the mobile retroreflectometer is more complicated than the portable retroreflectometer.

To achieve an accurate calibration with any mobile retroreflectometer, the retroreflectometer needs to be properly mounted to the vehicle to achieve the proper measurement geometry. The retroreflectometer should sit level to the roadway and be mounted at the proper height from the ground. The position of the retroreflectometer should be monitored to ensure the correct height is maintained as data collection progresses.

Mobile retroreflectometers have to constantly be monitored to make sure the front window does not get dirty. The front window of the retroreflectometer should be cleaned often. There are software settings that need to be monitored constantly during the data collection to achieve the most accurate measurements. These settings differ by mobile retroreflectometer manufacturer. Driver position on the road needs to be monitored so that the marking remains within the measurement area of the retroreflectometer. If the driver goes too far one way or the other, the marking will go outside the measurement width and the marking will not be read.

Evaluating low retroreflectivity markings is often difficult because the difference between the marking and the road surface may not be enough for the system to easily distinguish the marking. RRPMs need to be monitored so that they are not included in the pavement marking data. The software should filter out the RRPMs. Outside influences such as glare

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from the sun may limit when data collection can occur. A high level of glare will negatively impact the readings.

Rumble stripe markings and profile markings are easier to evaluate with mobile retroreflectometers since the retroreflectometer is not in contact with the marking.

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Mobile Retroreflectometer Specification Requirements

• Measurements using a mobile retroreflectometer are required forcontracts totaling more than 50,000 ft. of pavement markings. Forcontracts between 20,000 and 50,000 ft. portable or mobileretroreflectometers can be used.

• Mobile retroreflectometers and operators must be certified by theTexas A&M Transportation Institute Mobile RetroreflectometerCertification Program.

• Markings must be evaluated after 3 days but not later than 10 daysafter application.

• Retroreflectivity requirements are the same as for portablemeasurements (250—white, 175—yellow).

• Must coordinate with and obtain authorization from the Engineerbefore starting any retroreflectivity data collection.

Additional and more detailed information is provided in Part 2 of the guidance presentation, Pavement Marking Specifications Concerning Mobile Retroreflectivity, Item 666: Section 4.5.1. Mobile Retroreflectometer Measurements

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• Provide mobile measurements averages for every 0.1 miles unless otherwise specified or approved

• Take measurements on each section of roadway for each series of markings

• Measure each line in both directions for centerlines on two‐way roadways

• Furnish measurements in compliance with Special Specification, “Mobile Retroreflectivity Data Collection for Pavement Markings”

• Provider must inform the Engineer and TTI at least 24 hr. before taking measurements for each job

Additional and more detailed information is provided in Part 2 of the guidance presentation, Pavement Marking Specifications Concerning Mobile Retroreflectivity, Item 666: Section 4.5.1. Mobile Retroreflectometer Measurements

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• Section 3.3. Data File

• Section 3.4. Map

• Section 3.5. Video

• Providers are required to submit all three sets of information

• Not all districts require providers to submit all three data sets.

The special specification identifies each of the items that should be provided on the summary data file, map, and video.

Providers format their information in different ways. There is not a standard format that providers must follow. The files should contain the information listed unless not required by the district.

Some districts have not required the providers to submit the video files because they do not use them for evaluation purposes. It is a good idea to require the providers to collect the video, even if it is not submitted, in case any issues arise. The video serves as a log of the data collected and can be used to resolve issues in some cases.

These specification requirements are described in more detail in Part 2 of the guidance presentation.

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Mobile Retroreflectometer Data Output

• The newer model mobile retroreflectometers automatically output data files, video files, and map files that are linked by file name.

• Older systems require the user to process information to generate the map files, and the video files are often of lower quality.

• The data output from the retroreflectometers has the information needed to meet the TxDOT specifications; some modifications and formatting are required.

The districts need to make sure the providers are collecting and submitting the data in the way that they want before the project starts. The providers are required to submit data examples. If the submitted data do not meet the district needs, the output can be adjusted.

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Example Retroreflectometer Data FileFilename 79 yellow eb_2018‐06‐11_14_01_26.csv

Record Description Default_Route

Hardware ID Laserlux G7

Firmware Version 1.012_(Koufax)_1113_2021

Units English

Timezone Offset ‐5

Cal Factor 0.053917

Cal Standard Value 189

Cal IR Standard Value 28

Calibration Date and Time 2018‐06‐11_13:54:23

Stripe Colortype Yellow

Minimum Good Value 175

Minimum Marginal Value 175

Minimum Valid Value 55

Road Condition Label and Type 0 control_area on‐off

Road Condition Label and Type 1 debris on‐off

Road Condition Label and Type 2 sun_glare on‐off

Road Condition Label and Type 3 asphalt_tracking on‐off

Road Condition Label and Type 4 crack_seal on‐off

Road Condition Label and Type 5 intersection on‐off

Road Condition Label and Type 6 bridge on‐off

Road Condition Label and Type 7 wet on‐off

Road Condition Label and Type 8 dirty on‐off

Road Condition Label and Type 9 work_zone on‐off

Record # Odometer Date Time Latitude Longitude Vehicle Speed Temperature Humdity Valid_Scans_Left Retro_Left_Maximum Retro_Left_Minimum Retro_Left_Average Retro_Left_Stripewidth Retro_Left_Contrast RPMS_Found_Left StripeType Road_Conditions

0 0 6/11/2018 14:01:26 30.90902 ‐96.606827 54 95.58 34.00% Single_Solid

2 0.1 6/11/2018 14:01:33 30.91014 ‐96.605667 58 95.59 33.60% 2135 314.1 68.3 158.3 2.9 0.91 0 Single_Solid

4 0.2 6/11/2018 14:01:39 30.91119 ‐96.604546 60 95.79 34.10% 2278 273.8 111.3 177.7 3.7 0.92 0 Single_Solid

6 0.3 6/11/2018 14:01:45 30.91223 ‐96.603401 58 95.94 34.20% 1762 4615.1 67 191.4 3.7 0.92 24 Single_Solid

8 0.3 6/11/2018 14:01:46 30.91237 ‐96.603249 58 95.95 34.30% 172 166.6 61.9 107.7 2.6 0.93 1 Single_Solid

10 0.3 6/11/2018 14:01:49 30.91301 ‐96.602547 58 95.99 34.50% 810 246.1 60.3 134.1 3.1 0.9 10 Double_Solid

12 0.4 6/11/2018 14:01:51 30.91329 ‐96.602249 58 96.02 34.50% 536 6027.8 82.1 212.3 4.1 0.92 2 Skip_Right

14 0.4 6/11/2018 14:01:57 30.91425 ‐96.601219 58 96.14 34.00% 1275 283.3 65.8 150 3.2 0.91 5 Skip_Right

16 0.5 6/11/2018 14:01:57 30.91436 ‐96.601105 58 96.18 34.00% 35 202.1 82.1 128 3 0.92 1 Single_Skip

18 0.6 6/11/2018 14:02:03 30.91542 ‐96.59996 57 96.28 34.40% 519 330.1 70.3 121.2 3.1 0.92 6 Single_Skip

20 0.7 6/11/2018 14:02:10 30.9165 ‐96.598801 57 96.35 34.40% 553 188.6 72.5 121.3 3.1 0.94 8 Single_Skip

22 0.8 6/11/2018 14:02:16 30.91761 ‐96.597717 57 96.5 33.40% 507 181.3 64.7 118.7 3.3 0.93 7 Single_Skip

24 0.9 6/11/2018 14:02:22 30.91888 ‐96.596909 59 96.6 33.50% 601 211.5 64.2 127.8 3.4 0.93 7 Single_Skip

26 1 6/11/2018 14:02:28 30.92021 ‐96.59623 61 96.64 33.60% 523 227.5 65.7 125.2 3.6 0.95 7 Single_Skip

This is the direct Excel output from a mobile retroreflectometer. There will be additional columns to the right if the marking being evaluated is a double yellow centerline marking.

The output will be described in more detail on the next slide.

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Example Retroreflectometer Data File

Record # Odometer Date Time Latitude Longitude Vehicle Speed Temperature Humidity

Valid_Scans_Left

Retro_Left_Maximum

Retro_Left_Minimum

Retro_Left_Average

Retro_Left_Stripewidth

Retro_Left_Contrast

RPMS_Found_Left

StripeTypeRoad_Conditions

Driven distance (M)

Timestamp Logmark RL Left RL Center Left Width Left (inch)Daylight contrast Left

No of Roadstuds

Latitude (deg) N/S Indicator Longitude (deg) E/W Indicator Altitude (ft) Speed (mph) Course (deg)

• RoadVista Mobile Retroreflectometer

• Delta Mobile Retroreflectometer

The column header information presented represents some of what will be output. Each row of data will be the data collected over a segment length, typically 0.1 miles.

Both units output information on the time, number of measurements, distance, and GPS. There are some differences between the different types of retroreflectometers and what is directly output. The RoadVista unit provides the number of scans, maximum and minimum values for each section of data, and average value.

For the Delta unit, the RL Left and RL Center Left are data from the same marking, either the left of a double marking or from a single marking. The RL Left is the average across the width of the marking. The RL Center Left is the average across the central 2 inches of the marking. This value may better reflect the readings taken with a portable retroreflectometer. Large differences between these values indicate poor bead distribution across the marking. RL Right and RL Center Right are on the same marking but will be the right marking of a double marking or from a single marking.

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Example Summary Data FileSeries nam276 SH 6 DATE 01/17/2018

Direction SB DISTRICT Waco

Side WE COUNTY McLennan

Length (M 0 ROUTE # SH 6

Driven Len 8.8 DIRECTION SB

ReferenceNH 2017 (876) LINE TYPE WE

Comment County Mc Lennan LINE COLOR Wht

User nameFEC MATERIAL Thermo

Comment

Maximum 486 NUMBER OF READING 89

Minimum 231 INTERVAL PASSING 88

Standard D 49.72 443 INTERVALS FAILING 1

Average 373.2 430 PASSING % 99%

6.49 FAILING % 1%

436.92 TOTAL AVG OF LINE 373.20

SINGLE AVG 373.20

Driven dis TimestampLogmark RL Left RL Center Width LeftDaylight coNo of RoadLatitude (dN/S IndicaLongitude E/W IndicaDatum Fix descripNo of Sats Altitude (FSpeed (mph)

0 1/17/2018 429 442 5.14228 2.615571 0 31.55755 N ‐97.0978 W w84? Standard G 10 375.974 40.27471 1

0.1 1/17/2018 437 449 5.275897 2.484238 0 31.55641 N ‐97.0967 W w84? Standard G 10 374.3255 45.42676 1

0.2 1/17/2018 391 399 5.325254 2.40129 0 31.55536 N ‐97.0955 W w84? Standard G 9 375.6172 44.46297 1

0.3 1/17/2018 338 369 8.451391 2.653986 0 31.55452 N ‐97.0942 W w84? Standard G 10 380.177 44.57047 1

0.4 1/17/2018 358 368 5.058726 2.294161 0 31.5539 N ‐97.0926 W w84? Standard G 10 395.2233 41.7619 1

0.5 1/17/2018 257 260 4.818612 2.270113 0 31.55338 N ‐97.0911 W w84? Standard G 10 408.4446 42.01134 1

0

100

200

300

400

500

600

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 67 69 71 73 75 77 79 81 83 85 87 89

RL Value

Chainage

Reflectivity Readings

Single Avg

The summary file, as described in detail in Part 2, should contain the retroreflectivity dataand a graph of the data to show how the data change over the length of the marking. Other information as required by Special Specification 6291 needs to be included in the summary file. The providers should include the raw data with the summary file. The raw data are useful if there are issues with data quality or other issues that may be resolved by looking at the original data file.

In this summary file, the project information is in the upper right corner. The retroreflectivity for each 0.1‐mile segment is at the bottom and plotted in the graph. The retroreflectivity values are highlighted green because they exceed the 250 minimum retroreflectivity requirement.

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Example Map File

This example map file is from a white edge line marking. Each 0.1‐mile segment on the chart is color‐coded green because the average value in each section exceeded 250.

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Example Map File

This example map file is from one direction of a yellow centerline marking. Most of the 0.1‐mile segments on the chart are color‐coded red because the average value in those sections was below 175. The areas color‐coded green exceeded 175.

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Example Map File

This is a different style of map file for a double yellow centerline. The green value was set at 250 or greater, and yellow was set at 175 to 249, meaning everything above 250 would be green, 175–249 would be yellow, and <175 would be red. This yellow marking section had some failing and passing areas.

This instrument plots the left and right retro values for doubles lines on the same map (see the dividing line in the circles. The other retroreflectometers plot them in separate map files. This instrument also uses circles at the midpoint of the test segments instead of a continuous line between test segments.

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Example Video File

http://tti.tamu.edu/documents/facilities/visibility/mpmr-guidance/example-video-1.mp4

The video quality of these videos can be increased on the newer systems. They can take up a lot of space, so a balance between quality and video size needs to be made.

The videos in this presentation have had the quality reduced some to reduce the size of the presentation.

The various information boxes present the data associated with the data collection. The types of information provided in the boxes is not adjustable. Information provided on the video includes: Retro value, width, contrast value, count of RRPMs, file name, measurement direction, side of measurement, reference number, date, operator, total section length, segment length, time, and distance driven.

This video is from an evaluation of the yellow edge line.

A link to download or view the video is provided under the video image.

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Example Video File


This video is from a different retroreflectometer manufacturer. There is not as much descriptive information.

Date, time, file name, GPS location, chainage data, and retro values are provided in the text at the top.

This video is from an evaluation of the yellow edge line.


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Example Video File


This video is from the older style mobile retroreflectometer system and shows data collection at the certification test area.

The video shows file description; GPS location; chainage data; speed; operatingtemperature; RRPM cutoff level; retro values with max, min, average, and counts; date; and time.


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Summary

• Portable Retroreflectometers• Calibration

• Operation

• Requirements

• Data Output

• Mobile Retroreflectometers• Calibration

• Operation

• Requirements

• Data Output

This part of the guidance presentation covered the calibration, operation, specification requirements, and example data output from both portable and mobile retroreflectometers.

The providers need to know how to properly operate and maintain their equipment. The providers need to know what the specification requirements are, and TxDOT needs to make sure the providers are submitting data that meet its requirements. If providers have issues with equipment or issues with meeting specification requirements, they can contact TTI or the instrument manufacturer. If TxDOT wants additional information or a demonstration of the equipment, they can contact TTI who can arrange a demo.

This concludes the discussion of the pavement marking retroreflectivity equipment.

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Part 5:Retroreflectivity Data

Requirements and Analysis

(35–40 minutes)

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Retroreflectivity Data Requirements and Analysis Outline

• Specification Requirements

• Data Analysis• Data Interpretation• Summary Spreadsheet Data

• Map File

• Video File


• Common Issues

• Next Steps

We are going to focus on mobile retroreflectivity requirements and analysis in this part of the guidance presentation. Portable requirements have been described in other parts of the presentation. The analysis of portable measurements is similar to that of the mobile data, but there is a lot less data to evaluate, and the data may not be organized as well.

Some of these topics have been covered in other parts of the presentation. Part 2 of the guidance presentation covered the specification requirements in depth. Part 4 of the guidance presentation included information on data output. Part 3 included some information on comparing the data to requirements. This part of the guidance presentation will cover some of these areas in more detail. Where areas have been summarized, the part of the guidance presentation to reference for additional information will be mentioned.

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Item 666—Retroreflectorized Pavement Marking : Requirements

Special Provision 666‐007, Approved in February 2018

4.4—Retroreflectivity Requirements

• Required for Type I contracts totaling more than 20,000 ft. of markings

• White—250 mcd/m2/lux

• Yellow—175 mcd/m2/lux

• Measured 3–10 days after application

Detailed information on the specification requirements was covered in Part 2 of the guidance presentation. Specification information in this section is summarized.

Updated special provision required starting for May 2018 letting.

Contracts with total pavement marking quantities below 20,000 ft. are not subject to the minimum retroreflectivity requirements, unless shown on the plans. Callout work is not subject to the minimum retroreflectivity requirements unless shown on the plans.

Retroreflectivity requirements are 250 for white markings, whether they are solid or broken, and 175 for yellow markings, whether they are solid or broken. Yellow markings must meet requirements in both directions of travel when serving as a centerline.

Providers should evaluate the markings 3–10 days after application. This allows the markings to get some traffic to remove loose and excess beads. Readings after 10 days can still be accepted, but there should not be any leeway on the required retroreflectivity level.

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• Mobile retroreflectivity measurements are required for Contracts totaling more than 50,000 ft. of pavement markings

• For Contracts with 20,000–50,000 ft. of pavement markings, mobile or portable retroreflectometers may be used at the Provider’s discretion

• Coordinate with and obtain authorization from the Engineer before starting any retroreflectivity data collection

Mobile measurements must be used for all contracts with over 50,000 ft. of markings. Contracts with less than 50,000 ft. of markings may be evaluated with either mobile or portable retroreflectometers. Unless specified on the plans, contracts with less than 20,000 feet of markings do not require retroreflectivity readings.

Providers should obtain authorization from the Engineer before starting any retroreflectivity data collection.

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• Provide mobile measurement averages for every 0.1 miles unlessotherwise specified or approved.

• Take measurements on each section of roadway for each series ofmarkings (i.e., edgeline, center skip line, each line of a double line,etc.) and for each direction of traffic flow. Measure each line in bothdirections for centerlines on two‐way roadways (i.e., measure bothdouble solid lines in both directions and measure all center skip linesin both directions).

• Furnish measurements in compliance with Special Specification“Mobile Retroreflectivity Data Collection for Pavement Markings,”unless otherwise approved. Currently SS 6291.

• Inform the Engineer at least 24 hr. before taking any measurements.*

All longitudinal markings must be evaluated. Yellow centerline markings on two‐way roadways must be evaluated in both directions. For double yellow and broken/solid marking configurations, each marking must be evaluated separately.

References Special Specification 6291.

Engineer must be informed 24 hours prior to taking measurements. *SS 6291 requires that TTI be informed as well.

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• A marking meets the retroreflectivity requirements if:• the combined average retroreflectivity measurement for a 1‐

mile segment meets the minimum retroreflectivity values specified, and

• no more than 30% of the retroreflectivity measurement values are below the minimum retroreflectivity requirements value within the 1‐mile segment.

• The Engineer may accept failing 1‐mile segments if no more than 20% of the retroreflectivity measurements within that mile segment are below the minimum retroreflectivity requirement value.

• Centerlines with two stripes (either solid or broken) will result in 2 miles of data for each mile segment. Each centerline stripe must be tested for compliance as a stand‐alone stripe.

Analysis requirements are provided in this section. Data are to be analyzed in 1‐mile segments. The average over the mile needs to exceed the required values (250 white, 175 yellow), and no more than three of the ten, 0.1‐mile segments can be below the required value.

There is an exception: an overall 1‐mile average that is below the required value may be accepted if only two, 0.1‐mile segments are failing.

Information on restriping failed sections is provided in the specification. Those paragraphs are described later in Part 5 of the guidance presentation, during the Next Steps discussion.

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Special Specification 6291: Requirements

• Item 666‐007 Section 4.5.1. Mobile RetroreflectometerMeasurements• Furnish measurements in compliance with SpecialSpecification, “Mobile Retroreflectivity Data Collection forPavement Markings,” unless otherwise approved

• Special Specification 6291 covers the following• Equipment and Personnel• Mobile Retroreflectivity Data Collection Documentation

• Data File, Map, Video• Field Checks• Measurement Notification• Verification Testing• Referee Testing

Item 666 references the Special Specification by title, not number, since it may be revised. The current version is Special Specification 6291 and is required starting with May 2018 letting.

Many of the topics that Special Specification 6291 covers have been described in previous parts of this presentation. • Verification and referee testing was covered in depth in Part 3.• Specification requirements were covered in depth in Part 2.• Data, map, and video output were covered in general in Part 4.

This part of the guidance presentation will summarize the information on the specification requirements and go more in depth on the data output, how to interpret it, and how to compare to Item 666 requirements.

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Special Specification 6291: Marking Requirements

• Mobile Retroreflectometer—Certified by the TTI Mobile Retroreflectometer Certification Program

• Operating Personnel for Mobile Retroreflectometer—Certified by the TTI Mobile Retroreflectometer Certification Program to conduct MRDC with the certified mobile retroreflectometer provided

• https://groups.tti.tamu.edu/visibility/programs-and-guidance/mobile-retro-certification/certified-providers/

Equipment and personnel must be certified by TTI.

During the certification process, TTI will check any available portable retroreflectometers for accuracy at no additional charge.

MRCD = Mobile retroreflectivity data collection

The certification list is updated frequently and should be checked prior to allowing work on any new jobs.

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• Preliminary Documentation Sample—A sample data file,video, and map of MRDC data in the required formatshould be submitted for TxDOT review 10 working daysprior to beginning any work. The format must meetspecification and be approved by the Engineer before anywork may begin.

• Initial Documentation Review and Approval—TheDepartment will review documentation submitted for thefirst day of MRDC, and if it does not meet specificationrequirements, will not allow further MRDC untildeficiencies are corrected. The Department will inform theProvider no later than 3 working days after submittal if thefirst day of MRDC does not meet specificationrequirements.

For the most part, providers are not submitting and districts are not requesting preliminary documentation. This is not a new addition to the specification. Districts should request this information to make sure the providers are going to submit data in the proper format. Not all districts request all information contained in this specification, and providers may assume they do not need to deliver it all when working with a new district.

Districts need to review the initial documentation submission to make sure it fits their needs. If it does not, the provider needs to be notified as soon as possible so that they can modify the documentation as needed.

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• Measurement Notification—Provide notification via email to [email protected] a minimum of 24 hours prior to mobile retroreflectivity data collection to allow for scheduling verification testing when needed.

• Data Submission—All collected data should be submitted to the Department and to the TTI Mobile Retroreflectometer Certification Program no later than 3 working days after the day the data is collected. Submit all raw data collected in addition to all other data submitted.

Item 666 requires that the engineer be notified at least 24 hours in advance, and Special Specification 6291 requires that TTI be notified as well. Notification of TTI is a new addition to the specification. TTI needs to be notified for all projects.

Districts are also welcome to notify TTI if they are having issues or would like a provider checked.

From TTI’s perspective, it would be ideal if providers submitted weekly work plans on Monday, instead of daily plans every day. This weekly work plan would indicate which roads they are planning to read, what job those readings are part of, and when those roads were striped. There is an understanding that these plans may change some due to delays or weather. The 3–10 day window still needs to be met; any delays beyond that are on the provider and cannot be used as an excuse for failing readings.

Data submission: It is necessary to get the data within 3 days so that retroreflectivity values can be verified if needed. If the provider delays submitting the data, there will be a longer time span between provider‐collected data and verification/referee testing. This longer time span may result in changes to the retroreflectivity and increase the difference between the data sets.

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Summary Spreadsheet Requirements (Data File)

• date; • county;• name of mobile retroreflectometer operator; • route number with reference markers or other reference information provided by the

Engineer to indicate the location of beginning and end data collection points on that roadway;

• cardinal direction; • line type (single solid, single broken, double solid, etc.); • line color; • file name corresponding to video; • average reading taken for each 0.1‐mi. interval (or interval designated by the Engineer); • accurate GPS coordinates (within 20 ft.) for each interval; • color‐coding for each interval indicating passing or failing, unless otherwise directed by the

Engineer; • graphical representation of the MRDC (y‐axis showing retroreflectivity and x‐axis showing

intervals) corresponding with each data file; • distance in miles driven while measuring the pavement markings; • event codes (pre‐approved by the Engineer) indicating problems with measurement; • portable retroreflectometer field check average reading and corresponding mobile average

reading for that interval when applicable;

Special Specification 6291 outlines the specific requirements for the summary data file.• The summary data file should be in an electronic file in spreadsheet format.• The summary data file should have the accompanying raw data used to produce the

summary data file.

Part 2 of the guidance presentation and the Special Specification itself outline all of the requirements of the data file. The list presented here highlights some of the more important information.

Providers format their data files in different ways. There is not a standard format that providers must follow. The files should contain the information listed unless not required by the district.

There are some differences between mobile retroreflectometers, their software, and their output data that may affect some of the above required items.

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Data Mapping Requirements• Provide a map in an electronic format approved by the Engineer with each MRDC submission that includes the following information: • date; • district number; • county; • color‐coded 1‐mi. intervals (or interval length designated by the Engineer) for passing and failing retroreflectivity values or retroreflectivity threshold values provided by the Engineer; and

• percentage of passing and failing intervals, if required by the Engineer.

Each of these items should be provided on the map file.

Providers format their map files in different ways. There is not a standard format that providers must follow. The files should contain the information listed unless not required by the district.

There are some differences between mobile retroreflectometers, their software, and their output data that may affect some of the above required items. Most of the providers are submitting map files generated directly by the software provided with their mobile retroreflectometer. There is not much room to change these files. TTI has worked with the equipment manufacturers to try to get the data in alignment with the specifications. Most map files have the data color‐coded by the length of the data acquisition interval (i.e. typically 0.1‐mile segments).

The italicized bullets are not really necessary for data organization or evaluation purposes.

Information on percent intervals passing or failing is not necessarily needed on the map files, since it is part of the data file.

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Video Requirements

• The specification calls for a high‐quality DVD or electronic video file. The electronic file is typically preferred due to ease of transferability.

• The following information should be on the video.• retroreflectivity values presented on the same screen with the following information: • date; • location; • starting and ending mileage; • total miles; • retroreflectivity readings.

Each of these items should be provided on the video file. The specification indicates a DVD, but electronic files are preferred. The new equipment provides electronic files that are simple to transfer and of good video quality.

Part 2 of the guidance presentation and the Special Specification itself outline all of the requirements of the data file. The list presented here highlights some of the more important information.

Generally, the video file name will indicate the route, start and end points, direction of travel, and project number.

Providers format their video files in different ways. There is not a standard format that providers must follow. The files should contain the information listed unless not required by the district.

There are some differences between mobile retroreflectometers, their software, and their output data that may affect some of the above required items. Most of the providers are submitting video files generated directly by the software provided with their mobile retroreflectometer. There is not much room to change these files. TTI has worked with the equipment manufacturers to try to get the data in alignment with the specifications.

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Data Interpretation

• Summary Spreadsheet

• Data Map File

• Video File

In this section, we will discuss interpretation of the submitted data. This was covered briefly in Part 4 of the guidance presentation but will be covered more in depth here.

Each of the three forms of submitted data will be explored.

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Summary Spreadsheet Information

• File name should clearly indicate what data are being presented

• The spreadsheet should have at least two tabs:• One tab should have the raw unedited data that were collected

• One tab should have the required summarized data based on SS 6291

• A chart showing the data should be presented to allow easy visual analysis of the data

These are the basic components of the data sheet. Some systems and contractors add to the raw data sheet to meet the requirements. In this case, a single tab is sufficient per marking. Within the data sheet, the data should be summarized to meet the requirements of Special Specification 6291. The chart should show the retroreflectivity values along the entire length of the marking being evaluated.

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Mobile Retro Data File Example

This is an example of a summary data file. Much of the required project information is in Columns A and B rows 1 through 11. This information provides location, marking type, and job details. An overall summary of the data is provided in Rows 14 through 17. Row 18 indicates the file name of the associated map file. Rows 19 through the bottom of the file provide the retroreflectivity data. Column A indicates the distance driven, Column B has the time with imbedded data, and Column C provides any log markings if the operator made any notes in the data during data collection. These log marks are associated with the entire 0.1‐mile long segment, even if they may have only lasted a short distance with that span. Columns D and E provide the retroreflectivity values for the left pavement marking (if two were present). Column D is the retro value across the whole width of the marking, and Column E is the retro value across the middle 2 inches of the marking. Columns F and G provide additional information that is not required on marking width and daylight contrast. These values have not been well studied to judge their accuracy. Columns H through K provide the same marking information but for the right line, if there were two adjacent lines. Column L provides a count of RRPMs; this value has not been studied to determine its accuracy. GPS information is provided in columns to the right of what is displayed.

A plot of the retroreflectivity vs. distance driven is provided. The green line indicates the left marking, and a red line indicate the right marking. This is a white edge line marking, so the readings meet the minimum retroreflectivity level of 250. The spreadsheet does not show the percent passing and failing the minimum value. The spreadsheet is also not using color to indicate passing or failing of the average values. Since all the data are passing, this is not a big issue. If the data were a mix of passing and failing, the colored values would

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make it easier to visually see the areas with passing and failing readings.

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This is another example of a summary data file. This example is similar to the previous one, except that it is for a double line, and a different mobile retroreflectometer system was used, so the data output is a little different. The location, marking type, and job information are provided in the upper left portion of the table. The retroreflectivity data are provided in the bottom half of the spreadsheet. The interval column indicates the distance driven. The stripe type column indicates the type of double marking (double solid, skip right, skip left, or single skip). The points column indicates the number of readings recorded per segment. The left and right average values are the average retro values for the left and right markings for each segment. The stripe average column is the average of the two average values. The time and GPS coordinates are provided. The event code column indicates any notes the operator made during the data collection.

A plot of the retroreflectivity vs. distance driven is provided. The solid line indicates the left average value, and the dashed line indicates the right average value. The spreadsheet is not using color to indicate passing or failing readings, though the retro requirements are noted in the upper right portion of the spreadsheet.

These data are clearly not all passing, so the color‐coordinated values would be beneficial in visually analyzing the data. The majority of the data appear to be failing. Ways to analyze the results are provided later in this portion of the presentation .

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This slide shows a chart associated with a summary data file. The spreadsheet has a chart tab, a data tab (summary data), and a raw data tab. The chart has a horizontal line drawn at 250 indicating the required retro level. All the data are clearly passing on this white skip line.

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This is the second tab, the data tab, from the previous slide. This tab contains the summarized data and project information.

The chainage column indicates the distance driven. The center columns are separated for the different line types: white broken, white solid, yellow solid, yellow broken. The average value for the marking is provided. The GPS information and event codes are also provided. This chart indicates the percent passing and failing the minimum retroreflectivity level. The green highlighted values indicate passing retroreflectivity levels.

The raw data tab contains additional information that is automatically output by the retroreflectometer software. That information is not really needed for the evaluation of this marking.

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Map Information

• File name should clearly indicate what data are being presented.

• The map provides a visual tool to analyze the quality of the striping.

• Most maps are provided in Google Earth format. Multiple maps can be displayed at once.

Not much information needs to be in the maps. If the file name is adequate, the map itself can just display the data with appropriate color for passing and failing data.

In Google Earth, multiple .kmz or .kml files can be opened at once and displayed at the same time. This will be described in more depth later in this section.

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Mobile Retro Map File Example

The newer mobile retroreflectometers directly output Google Earth files; these are .kml or .kmz files. These files can be viewed directly in the free Google Earth software.The map file here has been opened and fully displayed in Google Earth. The data presented are for one of the yellow centerline markings on the road. Yellow centerlines that contain two lines will be displayed in separate maps with the output from this system. The other system produces a single map.

Green indicates greater than 175, yellow is 174–175 and red is less than 174.

The data are presented in 0.1‐mile segments, which is the distance over which the data were aggregated. Individual segments can be selected to display the actual values, which are listed on the left hand side of the screen.

These data have mixed results with a portion of the markings falling below the required level of 175. This area would need further evaluation, by looking at the summary spreadsheet, to determine if restriping is necessary. Evaluating the data will be described later in the presentation.

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Mobile Retro Map File ExampleMobile Retro Map File Example

This map displays the map data output from the other major manufacturer of the mobile retroreflectivity equipment. Again, Google Earth is used.

This instrument plots the left and right retro values for doubles lines on the same map (see the dividing line in the circles where the system picked up a second stripe). The other retroreflectometers plot them in separate map files. This instrument also uses circles at the midpoint of the test segments instead of a continuous line between test segments.

These data are for a white edge line. Green indicates data 250 mcd/m2/lux or more. Red indicates data under 250 mcd/m2/lux.

This section had some failing and passing areas. The areas with failing readings were all the locations where a second line was detected. These are likely errant readings near intersections and were not actual readings of the new pavement markings.

Individual data points can be selected, as shown (white callout box), to display the retroreflectivity value and much of the other information that can be found in the summary spreadsheet.

The white dots indicate 0.1‐mile segments in which no markings were detected.

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Instead of submitting a google map file, this provider took a screen capture of the google map. The provider overlaid project information, the white text at the top, onto the file.

The data are for a white skip line marking, passing retro levels. Green indicates values over 250.

Data submitted like this meets specification and may be easier for TxDOT in some ways, but it also limits some of the flexibility of having the actual Google Earth file.

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As previously mentioned, multiple Google Earth files can be displayed at once.

This map displays data TTI collected on in‐service markings around Houston. The map displays the white edge line markings on the main lanes for the evaluated roads.• Green >200• Yellow 150–200• Red <150

Displaying multiple roads together can help determine which roads may need to be restriped based on retroreflectivity levels.

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Video Information

• File name should clearly indicate what dataare being presented

• The video provides a visual tool to review ifissues with the data arise

• Most videos are provided in typical video fileformats

Not much information needs to be in the videos. If the file name is adequate, the video itself can just display the retro, GPS, and mileage data.

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Video File Example

http://tti.tamu.edu/documents/facilities/visibility/mpmr-guidance/video-file-example-1.mp4

The quality of these videos can be increased on the newer systems. They can take up a lot of space, so a balance between quality and video size needs to be made.

The videos in this presentation have had the quality reduced some to reduce the size of the presentation.

The various information boxes present the data associated with the data collection. This type of information is not adjustable, but the content inside the user entry areas can be changed.• Retro value, width, day contrast value, and count of RRPMs are all in the upper left.• File name, measurement direction, side of measurement, reference number, date,

operator, total section length, and segment length over which the data are aggregatedare at the bottom left.

• Time and distance driven are at the bottom right.

The horizontal green lines are provided to indicate the distance at which the measurements are being made.


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Video File Example


This video is from a different retroreflectometer manufacturer. There is not as much descriptive information.

Date, time, file name, GPS location, retro values, and chainage data are provided in the text at the top.

This video would be of better quality if the operator did not have the white paper on the dash, which is reflecting on the windshield.

This video also shows the operator passing a vehicle that pulled out in front of him/her. The retro values stopped when the vehicle passed because the operator paused the data. When the operator got back to the edge line he/she unpaused the data, and collection resumes. In the data spreadsheet, there will not be any data collected for the 0.1‐mile segment during the pass. The video can be used to determine why there is missing data or to verify notes the operators make during data collection.


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Video File Example


This video is from the older style retroreflectometer.

The video file shows description; GPS location; chainage data; speed; operatingtemperature; retro values with max, min, and average; and counts.


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Comparing Data to Requirements• Retroreflectivity Requirements:

• White markings: 250 mcd/m2/lx• Yellow markings: 175 mcd/m2/lx

• A marking meets the retroreflectivity requirements if:• the combined average retroreflectivity measurement for a 1‐

mile segment meets the minimum retroreflectivity valuesspecified, and

• no more than 30% of the retroreflectivity measurement valuesare below the minimum retroreflectivity requirements valuewithin the 1‐mile segment

• The Engineer may accept failing 1‐mile segments if no morethan 20% of the retroreflectivity measurements within thatmile segment are below the minimum retroreflectivityrequirement value

The retroreflectivity requirements and what constitutes meeting the requirements are in Item 666.

Each line has to meet the requirements. Yellow centerlines need to be evaluated separately.

In summary, a 1‐mile segment will meet requirements if the average retroreflectivity value over that mile meets or exceeds the required values, and no more than 30% of the values are below the minimum value. That means seven of the ten, 0.1‐mile segments need to meet or exceed the minimum value, and the average for the whole mile needs to meet or exceed the minimum value. Alternatively, if the average for the mile does not meet the minimum required value, but only two of the 0.1‐mile segments are below the required value, then the mile section can pass requirements.

The mile segments and some data are discussed on the next few slides.

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Comparing Data to Requirements

• The 1‐mile segment will start from the beginning of the data collection and end after a mile worth of measurements has been taken; each subsequent mile of measurements will be a new segment. Centerlines with two stripes (either solid or broken) will result in 2 miles of data for each mile segment. Each centerline stripe must be tested for compliance as a stand‐alone stripe.

This information is directly from Item 666. Data are to be analyzed in 1‐mile segments. This portion of the specification clearly indicates that yellow centerlines need to be evaluated separately.

Generally, all data are collected in 0.1‐mile increments. Unfortunately, the data are not always perfect because there are not always ten segments per mile. When evaluating yellow centerlines and the line type changes from one type to another, the software will create a new line of data when the operator changes the line type (for some equipment types). This will result in some segments shorter than 0.1 miles and more than ten segments per mile. If these areas are near the minimum retroreflectivity level, then additional effort is required to properly evaluate them. An example is provided during the data analysis on the next slides.

Information on restriping failed sections is provided in the specification and will be described during the Next Steps discussion later in this section.

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Driven distance (M) RL Center Left Averages

4 169

4.1 165

4.2 174

4.3 180

4.4 179

4.5 181

4.6 180

4.7 178

4.8 168

4.9 172

5 181

5.1 184

5.2 188

5.3 188

5.4 185

5.5 191

5.6 192

5.7 195

5.8 183

5.9 161

6 165

6.1 181

6.2 192

6.3 200

6.4 183

6.5 191

6.6 174

6.7 180

6.8 182

6.9 167

Yellow Edge Line

175

185

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Driven distance (M) RL Center Left Averages

0 139

0.1 176

0.2 253

0.3 316

0.4 216

0.5 291

0.6 367

0.7 381

0.8 383

0.9 334

1 260

1.1 269

1.2 271

1.3 272

1.4 268

1.5 175

1.6 184

1.7 259

1.8 261

1.9 265

2 377

2.1 431

2.2 389

2.3 411

2.4 360

2.5 380

2.6 361

2.7 374

2.8 384

2.9 389

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White Edge Line

Presented on this slide are two sets of data: One for a yellow edge line marking and one for a white edge line marking.

Both sets of data contain 3 miles of retroreflectivity data. The data are broken down by the mile and averaged in the column on the right. The individual 0.1‐mile segments have been color coded green for above 175 or 250, passing, and red for below, failing. The 1‐mile averages have been color‐coded for passing requirements, green, and failing requirements, red.

The first mile of the yellow data has an average of 175 but has five segments failing so the whole mile fails. The other 2 miles of yellow pass because they have an average of at least 175 and three or fewer failing segments.

The 3 miles of white data are all passing because each is at 250 or above and contains no more than three failing segments or has fewer than two 0.1‐mile segments failing.

Analysis like this should be conducted for each mile of each data set. For some markings that easily meet the minimum, in‐depth analysis is not needed. Visually, the 1‐mile segments could be observed on the graphical representation of the data, or the rows of data could be looked at and determined to pass or fail without calculating out each mile average. If markings look like they may fail, it is a good idea to determine the averages to support your position.

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Chainage Stripe Type Left Avg Right Avg 1‐mile 1‐mile

0 Double_Solid Left Avg Right Avg

0.1 Double_Solid 74 82



0.4 Skip_Right 135 131


0.6 Single_Skip 192

0.7 Single_Skip 207

0.8 Single_Skip 181

0.9 Single_Skip 160

1 Single_Skip 191

1.1 Single_Skip 192

1.2 Single_Skip 189

1.3 Single_Skip 176

1.4 Single_Skip 142

1.5 Single_Skip 181

1.6 Skip_Left 170 185




2 Skip_Right 120 127

2.1 Skip_Left 254 260

2.2 Skip_Left 206 200






2.8 Skip_Left 229 240

2.9 Skip_Left 224 232

3 Skip_Left 175 164

Yellow Center Line

160 138

163 163

184 189

Presented on this slide are data for a yellow centerline marking. Each line of a yellow centerline needs to be evaluated separately and for each direction of travel. Only one direction of travel is shown here.

Like the previous slide, all of the data has been color‐coded for ease of analysis. Both lines for the first 2 miles fail. The averages are not high enough, and there are too many failed segments. One issue that will occur with yellow centerline markings is not having full sets of data for both lines all the time. In this data set there is a single skip line for a portion of each of the first 2 miles. For cases such as these the average still needs to occur in the 1‐mile segments from the start of the project. This may result in less than 1 mile of marking being averaged; in this case, both sections are about 0.5 miles. Their average still needs to meet or exceed 175, and no more than 30% of the individual segments (1 or 2 segments) can fail for the section to be accepted. If there are very few sections and the average value is close, engineering judgment can be used to determine if restriping is needed. For double lines, if one line passes and the other line is close, then the marking may be acceptable. The measurements in the opposite direction along that same section may be the determining factor.

The third mile of data indicate that the left line passes and the right line is close. The right line is close because the average exceeds the requirement, but four segments are failing, which is one more than allowable. Engineering judgement can be used in this circumstance. If this is an isolated instance of lower retroreflectivity values, then it can be accepted. If there are frequent instances of low retroreflectivity and many other areas are

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requiring restriping, then requiring restriping may be advisable.

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Odometer StripeType Valid_Scans_Left Retro_Left_Average Valid_Scans_Right Retro_Right_Average

0 Double_Solid

0.1 Double_Solid 2925 409 2996 384

0.1 Double_Solid 2165 436 1946 330

0.2 Skip_Left 201 254 631 344

0.2 Skip_Left 839 364 1924 378

0.3 Double_Solid 873 356 896 345

0.4 Double_Solid 2783 364 2775 328

0.5 Double_Solid 2597 299 2538 334

0.6 Double_Solid 2303 364 2636 391

0.7 Double_Solid 2433 351 2608 369

0.8 Double_Solid 2232 395 2450 416

0.9 Double_Solid 2617 373 2608 353

1 Double_Solid 2635 323 2722 311

1.1 Double_Solid 2487 377 2576 350

1.2 Double_Solid 2071 391 2228 387

1.3 Double_Solid 2251 389 2570 401

1.4 Double_Solid 2617 402 2720 378

1.5 Double_Solid 3006 365 3047 343

1.6 Double_Solid 2777 302 2873 264

1.7 Double_Solid 2420 402 2562 376

1.7 Double_Solid 1526 374 1144 384

1.8 Skip_Right 959 374 258 348

1.9 Skip_Right 2394 419 577 348

1.9 Skip_Right 842 353 672 353

2 Skip_Left 417 381 1567 383

Yellow Center Line

Presented on this slide are data for a yellow centerline marking. Another issue when analyzing yellow centerline markings is uneven segment sizes. The retroreflectivity of these markings clearly exceeds the requirements, so segment size differences is not a big concern with these data, but it makes analysis more complicated if the data were closer to the requirements.

In the odometer readings, some of the values are repeated. This generally occurs when the pavement marking pattern type changes, and the operator notes it in the data. Sometimes values in between the tenth of a mile length are listed (i.e. 0.13). This can add more detail to the data set but results in uneven segment lengths. Accompanying the odometer and retroreflectivity readings are the number of valid scans. This is how many retroreflectivity readings are being averaged in each segment. Skip lines will have fewer readings than solid lines due to less marking being on the road. The left and right counts may not always be even due to stripe configuration, vehicle wander, and the system losing some readings on the left marking if the crown of the road is sharp. Generally, the data default to the left, so with double lines, the left line will typically have more unless the center of the road has a steep crest.

With uneven segment lengths, the markings still need to be evaluated in 1‐mile segments. There will just be more than 10 segments per mile. It may be necessary to combine the partial segments based on the number of scans to properly account for quantity measured if the retroreflectivity levels are different between the segments.

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Only one manufacturer of the mobile equipment allows for line type selection for centerline markings, so unequal segment size does not occur with data from the other manufacturer.

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Chainage Stripe Type Left Points Left Peak Average Right Points Right Peak Average Right Peak Standard Deviation Two‐Stripe Average

11.026 Single Skip 31 171 4 83 25 127

11.132 Single Skip 31 155 3 104 25 129

11.237 Single Skip 33 154 3 72 17 113

11.342 Single Skip 26 150 2 80 31 115

11.449 Single Skip 39 123 3 115 25 119

11.522 Left Skip / Right Solid 5 73 24 122 69 98



11.746 Left Solid / Right Skip 46 165 14 144 112 154

11.761 Left Solid / Right Skip 3 105 105



12 Single Skip 17 99 5 127 59 113





12.282 Double Solid 8 172 6 181 30 176




12.557 Single Skip 45 116 11 138 56 127

12.592 Single Skip 9 105 105

12.699 Single Skip 25 134 134

12.802 Single Skip 34 113 2 28 17 70

12.908 Single Skip 22 159 159

Yellow Center Line

Similar to the last slide, the data presented on this slide are for a yellow centerline marking. Again, the centerline line type is changed resulting in unequal segment sizes. The retroreflectivity of these markings is fairly poor, so further analysis is not necessary, but if the data were closer to the requirements, the data analysis would be a little more complicated.

The odometer readings in this data set show that the values are not in even 0.1‐mile intervals. The segments are starting at whatever chainage the odometer is at when the stripe type is changed. Again, accompanying the chainage and retroreflectivity readings is the number of valid scans (left and right points). This is how many retroreflectivity readings are being averaged in each segment. The left and right counts may not always be even due to stripe configuration, vehicle wander, and the system losing some readings on the left marking if the crown of the road is sharp. In some cases in the data, there are right points for single skip lines; sometimes this occurs when evaluating edge lines as well. The system picks up a few readings from rumble strips, markers, or other reflections, and the data get recorded. The operators should remove this extraneous data when creating the summary spreadsheet.

With uneven segment lengths, the markings still need to be evaluated in 1‐mile segments. There will just be more than 10 segments per mile. It may be necessary to combine the partial segments based on the number of scans to properly account for quantity measured if the retroreflectivity levels are different between the segments.

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These data are from the older retroreflectometer system; the number of data points collected is around 10% the number of data points collected by the newer system. That means the newer system is getting much better coverage of the pavement markings (i.e. more readings along the length of the marking).

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This summary data sheet provides data for a yellow centerline marking. The blue line in the graph is the left average, and the red line is the right average. In the graph, the variability of the data is apparent, with large swings up and down. This is typically not a good sign for the quality of the data collection or the quality of the marking. Some of the large drops to zero are because the data that were missing on the single skip areas where there was only a single line were plotted as zeros. This is incorrect; the zero data should not have been plotted. The line would not be continuous, but it wouldn’t spike down to zero when there was actually no reading to plot.

If just looking at the average of the data, it looks good. However, there are two apparent issues that require further exploration. Outside of the plotting of the missing data, the average values are still highly variable, and the average values for yellow thermoplastic are abnormally high. Typical yellow thermoplastic will range between 150 and 300. Readings over 300 are not too common. For white markings, the expectation is typically 350 to about 450.

The next slide will look at the raw data tab to try to explain some of the issues with these data.

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This is the raw data tab that was used to create the summary table and chart from the previous slide. The number of points (Column D and J) and the average values (Column G and M) were provided on the previous slide. In addition to the average retro data, we now have the left and right line max and min values along with their standard deviations. The standard deviation provides a measurement of how variable each of the average values is. This variability is influenced by the min and max values. Having a large range between the min and max values, coupled with a large standard deviation, means that the data are spread out. A good pavement marking should be relatively consistent, and good data collection should not negatively influence that consistency.

The very high maximum values likely indicate that RRPMs were not properly filtered out of the data. This will result in artificially high retro values, high maximum values, and high standard deviation values. The consistently very low minimum values likely indicate that the settings were not optimized to filter out background noise or that the markings were very poor. The variation between the maximum values in the different rows of data show there were some issue with the data collection. If you look at the rows that had the lower maximum values (values closer to where you would expect yellow markings to be), the average value for these sections are somewhat more reasonable.

Not all of the mobile retroreflectometers output the maximum, minimum, and standard deviation values. This may limit the ability to do this more in‐depth analysis for the data for some systems. The system that does not include these values does not have user adjustable settings; therefore it typically does not have this issue.

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Common Issues to Look for When Evaluating Provider‐Supplied Mobile

Retroreflectivity Data• Readings taken outside the 3–10 day window• Not submitting all data• Whether yellow centerlines were evaluated in bothdirections

• Low yellow retroreflectivity values• Left vs. right readings• Inconsistent segment lengths• Questionable data (high values, high variability)• Reading RRPMs• Dirty markings (dirt, seal coat, milling rumbles, etc.)

Readings taken outside the 3–10 day window: There are several reasons why readings may be taken after the 3–10 day window; for example weather delays, other projects, equipment issues, etc. may delay readings. This doesn’t mean they do not need to be taken, nor does it change the required retroreflectivity levels. Markings that are read after 10 days are more likely to have been subjected to more wear, and thus it is typically not an advantage for the provider to delay readings. Therefore later readings should be allowed, and if the measurements pass, then the markings can be accepted. If readings are taken before the third day, the markings are likely to have seen minimal wear and have a higher retroreflectivity value than if they were evaluated during the specified time period.

Not submitting all data: The specification requirements have been discussed in multiple parts of this guidance presentation. Part of the requirement is to submit example data prior to starting work. At this time, the data should be reviewed to make sure the required information is being submitted. If it is not, the provider needs to be made aware so it can submit the correct data. Providers should submit the raw data in addition to the summarized data. All markings need to be evaluated.

Yellow both ways: Providers are required to evaluate yellow centerlines in both directions. Both directions need to meet the retroreflectivity requirements. Left edge lines, and two‐way left‐turn lanes only need to be measured in the direction of the through lane. It is typical that the retroreflectivity values for yellow centerlines are lower when evaluated in the opposite direction of the application. This is especially true for seal coat roadways. The large profile of the seal coat aggregate and the forward velocity of the striping operation

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typically result in the thermoplastic and beads hitting the front side of the aggregate but less hitting the back side since it is somewhat shadowed from the aggregate vertical profile. This issue is made worse if contractors are going too fast and/or are not applying enough thermoplastic and beads.

Low yellow retroreflectivity values: Typically, yellow markings are not as reflective as white markings. The most difficult marking to install is a yellow centerline marking on a new seal coat roadway. The retroreflectivity readings are commonly low unless the providers are using quality materials and do a good installation job. If materials are not of good quality and/or the installation quality is not good, then the retroreflectivity levels will be low, especially in the direction opposite of the installation direction (see yellow both ways). Just because it may be more difficult to install yellow centerline markings on seal coat surfaces does not mean that the retroreflectivity requirements should be relaxed or ignored.

Left vs. right readings: This point was recently discussed when analyzing the yellow centerlines. The old equipment defaulted all readings to the left position; thus, when evaluating double lines, the left line would always have more readings. The newer equipment is much better at properly assigning data to the right or left. The systems also gather much more data, so any differences are not a big factor overall. When markings are broken left and solid right, the right will have more readings. In some instances, the systems will pick up measurement noise or retroreflectivity off things that are not markings and record data that should be disregarded. These data to disregard are typically much less than the average retroreflectivity value being recorded.

Inconsistent segment lengths: This point was recently discussed when analyzing the yellow centerlines. Files with inconsistent segments need a little more attention when analyzing whether the data meet the requirements. The inconsistent length is due to new lines of data being started when the centerline type changes.

Questionable data: If the data seem questionable and you cannot determine a reason why, please ask TTI to look at the data. We can quickly review the data and determine if there are inconsistencies with typical data or if the provider needs to improve its operations. If there are issues with the provider or questionable data, request that TTI do a verification check on the provider’s work. The district can conduct its own field checks using portable retroreflectometers. Spot checks on segments with questionable data can be used to verify if the data are reasonably accurate. The spot checks should be conducted in as close proximity time wise to the provider’s mobile retroreflectivity readings as possible. When looking at the data, the most noticeable indicators of questionable data are high variability in the data and inclusions of RRPMs in the data.

Reading RRPMs: Readings RRPMs will create high standard deviation and false high average readings. Yellow centerlines and white skip lines will generally have RRPMs in place. The mobile retroreflectometers either automatically filter the RRPMs or the operator has to set a level at which the RRPMs will be filtered. The opposite to reading RRPMs is recording

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readings on the pavement between skip line markings. If the equipment and software are not operated properly, low retroreflectivity levels may be recorded in the gaps between skip line markings. This will create false low readings. This is detrimental to the provider because the markings are more likely to not meet minimum retroreflectivity requirements if this occurs.

Dirty markings (dirt, seal coat, milling rumbles, etc.): Depending on when readings are taken, there are many factors outside the control of the provider that may negatively influence the retroreflectivity readings. The providers should note these issues when collecting data, and they should be considered when determining whether to pass or fail markings due to retroreflectivity requirements. Dirt tracked onto markings, seal coat asphalt tracking onto markings, and damage to markings due to construction activities are common and not the fault of the striping provider. Some of these issues may be visible in the video file, or they may require a field inspection to verify.

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Next Steps—Non‐Acceptable Retroreflectivity

• If the markings do not meet the retroreflectivity requirements, Item666 states the following:• Restripe at the Provider's expense with a minimum of 0.060 in. (60

mils) of Type I marking if the marking fails retroreflectivityrequirements. Take measurements every 0.1 miles a minimum of 10days after this second application within that mile segment for thatseries of markings.

• Restripe again at the Provider's expense with a minimum of 0.060 in.(60 mils) of Type I marking material if the average of thesemeasurements falls below the minimum retroreflectivityrequirements. Take measurements every 0.1 miles a minimum of 10days after this third application within that mile segment for thatseries of markings. If the markings do not meet minimumretroreflectivity after this third application, the Engineer may requireremoval of all existing markings, a new application as initiallyspecified, and a repeat of the application process until minimumretroreflectivity requirements are met.

Failing 1‐mile segments need to be restriped at the provider’s expense until the retroreflectivity readings meet the minimum requirements. TTxDOT needs to hold the providers accountable to the specification requirements. This creates an even playing field for all providers and will result in higher‐quality pavement markings that are more visible at night.

Some providers are proactive and restripe short deficient sections prior to submitting data to TxDOT. This results in full mile segments that meet the requirements, reduces TxDOT’s need to critically analyze the data, reduces TxDOT’s need to require restripes, and reduces the provider’s costs for restriping whole sections or calling back equipment it may have moved on to other jobs. The end result is markings that meet the new stripe minimum retroreflectivity levels.

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Next Steps—Acceptable Retroreflectivity

• If the markings meet the retroreflectivityrequirements, the project can beapproved.

• Effective May 1, 2020, new requirementshave been added to SiteManager tocapture receipt and review of theretroreflectivity data.

Passing markings can be approved. There is a new SiteManager requirement effective May 1, 2020. It requires the engineer to create a sample and attach a SiteManager test report to show that he/she has received and reviewed the retroreflectivity data from the Provider.

Please contact Kristina Santos ([email protected]) at (512) 506‐5870 with any questions regarding these new requirements.

Additional information on the SiteManager requirements will be provided in future versions of this guidance presentation and in the FAQ section of the Programs and Guidance website.

https://groups.tti.tamu.edu/visibility/programs-and-guidance/frequently-asked-questions/

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Summary

• Specification Requirements

• Data Analysis• Data Interpretation• Summary Spreadsheet Data

• Map File

• Video File


• Common Issues

• Next Steps

This part of the guidance presentation covered a summary of the specification requirements and data analysis for mobile retroreflectivity.

The data analysis included discussion on the data in the spreadsheets and how to analyze them to meet specification requirements. The discussion included common issues to look for and how to identify these issues in the summary and raw data files. The use and benefit of the map and video files were also discussed.

The specifications have specific retroreflectivity values that need to be met. There are conditions and situations that will require engineering judgment to fairly determine if the markings are acceptable or not. There are many factors outside of the pavement marking contractors' control that may impact their retroreflectivity values. Equitable analysis from job to job and contractor to contractor is key.

When markings have been determined to not be acceptable, the markings should be restriped. If they are acceptable, the engineer needs to create a sample report and submit to SiteManager.

This concludes the discussion of the retroreflectivity data requirements and analysis.

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Part 6:Questions and Comments

(<5 minutes)

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Questions and Comments Outline

• TTI Mobile Retroreflectivity Website

• FAQs

• Contact Information

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TTI Programs and Guidance Websitehttps://groups.tti.tamu.edu/visibility/programs-and-guidance/

The images provide the site content for the mobile retroreflectivity certification program. The list of certified operators and equipment is provided on the site and is regularly maintained to reflect changes. The site is being updated to contain information about the verification program, mobile retroreflectivity guidance, guidance on other areas related to signs and markings, links to relevant documents, and FAQs.

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FAQs• https://groups.tti.tamu.edu/visibility/programs-and-guidance/frequently-asked-questions/

• Under Development.• As questions and comments from the guidancepresentation are submitted, responses will bedocumented in the FAQ section of the website.

• A PDF of questions, comments, and responseswill be posted on the website.

• Please send any comments or questions toa‐[email protected]

Frequently asked questions and responses are being developed as the guidance presentation is circulated and questions are submitted. The FAQs will be listed on the TTI website along with all of the guidance information.

https://groups.tti.tamu.edu/visibility/programs-and-guidance/frequently-asked-questions/

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Contact Information

Adam Pike, P.E.Associate Research EngineerTTI Signs and Markings Programa‐[email protected]‐317‐2136https://groups.tti.tamu.edu/visibility/programs-and-guidance/

John BassettMaterials and Tests [email protected]‐506‐5881

TTI and TxDOT points of contact.Questions or issues can be directed to both individuals.

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mobile retro guidance presentation v12

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