peer review of belvedere place traffic and parking …€¦ · november 20, 2015 page 3 of 20...

Traffic Engineering & Transportation Planning

TRAFFIC WORKS, LLC

11885 Aspen Heights Ct., Rancho Cordova, CA 95742 916.242.8990

www.Traffic-Works.com

P.1

November 20, 2015

Bob Goralka, PE Transportation Division Manager Marin County – Public Works 3501 Civic Center Drive, Room 304 San Rafael, CA 94903 [email protected] (415) 473-3076

PEER REVIEW OF BELVEDERE PLACE TRAFFIC AND PARKING STUDY

This letter presents the peer review of the W-Trans traffic study for Belvedere Place in

Strawberry, CA, as well as all other correspondence your department sent to our firm relating to

this project application. I have also watched the Board of Supervisors meeting videos to get

context to these documents and letters. The following letter report summarizes my findings and

recommendations concerning what steps the County should take relating to this matter.

Overview

The Belvedere Place Traffic and Parking Study, June 24, 2015, prepared by Whitlock & Weinberger

Transportation, Inc. was built on a set of “planning level” default traffic analysis assumptions that

in some cases, led to inaccurate level of service calculations. Observed LOS D/E conditions in the

field at the SR 131 / Redwood Frontage Road intersection do not match the LOS C conditions

reported in the traffic study. These differences can be attributed primarily to a lack of measured

intersection traffic operations data, such as “Saturation Flow Rate,” “Signal Cycle Length,” “Signal

Phase Timing,” and “Lane Utilization Percentages.” When these values are measured in the field

they can be compared to the standard default values built into traffic analysis software. If

significant differences exist the measured field values are used. Typically these factors are not

necessarily measured because of budget constraints in preparing traffic studies. These four

critical factors are discussed in more detail later in this report, and how they can significantly

affect the level of service calculation.

Caltrans Guidelines. The Belvedere Place Traffic and Parking Study was peer reviewed in light of

conformance to industry standard methods for traffic engineering and transportation planning,

mailto:[email protected]

Peer Review of Belvedere Place Traffic and Parking Study Prepared For Marin County Public Works

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contrasting it to what is typically expected in a traffic impact study with Caltrans facilities

potentially impacted. In general the study was prepared according to typical industry standards,

but the study scope and assumptions used in the analysis are primarily the subject of this review.

In the Caltrans’ GUIDE FOR THE PREPARATION OF TRAFFIC IMPACT STUDIES, Dec. 2002 policy

document1 it communicates that a traffic study scope involving State facilities should be based

on consultation between the lead agency and Caltrans. In this pre-study consultation the parties

agree upon the data necessary for the study analysis and the methods of analysis needed. For

example, if traffic volumes are very light and where the level of service is acceptable (LOS A/B),

and there are no existing operational problems, then a simplified “planning level” analysis based

on default factors for traffic might be appropriate. However, if there are existing traffic problems

that are known to the governing agencies and/or the general public, if traffic is heavy, then a

more detailed traffic operations analysis may be required. A traffic operations analysis would

require additional data collection and more sophisticated analysis methods to better describe

existing and potentially critical conditions.

Micro-Simulation Analysis May Be Needed. There are Multiple Methods of Analysis. In Section

V. TRAFFIC IMPACT ANALYSIS METHDOLOGIES of the Caltrans traffic study guidelines document,

there are twelve (12) different types of possible analysis procedures listed that need to be

considered for possible inclusion in any traffic impact study, depending on the situation. Caltrans

guidelines do not specifically require a micro-simulation for projects that generate 1 to 49 peak

hour trips to an assigned highway facility, but these details are to be determined at the outset of

the traffic study scope development in consultation with Caltrans.

The Caltrans document states: “When a State highway has saturated flows, the use of a micro-

simulation model is encouraged for the analysis (please note however, the micro-simulation

model must be calibrated and validated for reliable results). Other analysis methods may be

accepted, however, consultation between the lead agency, Caltrans and those preparing the TIS

is recommended to agree on the data necessary for the analysis.”

Each procedure of traffic analysis covers specific problem areas such as freeway segments,

weaving areas, two-lane highways, pedestrians, bikes, signalized intersections, etc., which are all

analyzed differently and with different kinds of data. For intersections, an operations analysis

may be needed when there are traffic flows at or nearing capacity, or when intersections are

closely spaced such as is the case with the SR 131 and US 101 interchange location. At this

location there are four intersections closely spaced, each being signalized in a coordinated timing

system. The SR 131 / Redwood Highway Frontage Road intersection have saturated flows, as do

the freeway ramp intersections, so the use of a micro-simulation model such as SimTraffic is

encouraged for the analysis.

1 See http://www.dot.ca.gov/hq/tpp/offices/ocp/igr_ceqa_files/tisguide.pdf

http://www.dot.ca.gov/hq/tpp/offices/ocp/igr_ceqa_files/tisguide.pdf


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Planning Level Analysis vs. Operations Level Analysis. It is the conclusion of this peer review

that the traffic study prepared for the Belvedere Place project started out independently as a

simple planning level analysis for three (3) intersections only, and then after public review and

additional traffic concerns raised, evolved into a more lengthy set of data for seven (7)

intersections. Even still, the report/study remained a planning level analysis and did not take into

consideration the use of traffic operations analysis methods and operational data to adequately

assess the true intersection traffic impacts and potentially needed mitigations for the Belvedere

Place project. For instance, the entire interchange set of four intersections should have been

studied as a group of intersections with micro-simulation since they are inter-connected by

specific signal timing and since they are very closely spaced, as per Caltrans guidelines. Then the

traffic study could better ascertain whether the project traffic would significantly impact the

interchange operations and queue lengths, or not. The Highway Capacity Manual (HCM) analysis

procedures (used in the traffic study’s TRAFFIX software analysis) do not handle analyzing the

operational effects of closely spaced intersections, which exist at the US 101 interchange with SR

131. The entire set of four interchange intersections should have been studied additionally with

a micro-simulation software tool such as SynchroPro/SimTraffic, fully calibrated and validated by

Caltrans as per Caltrans’ guidelines. These tools require more detailed traffic data such as field

measurements of saturation flow rates (SFR) for each approach to an intersection, measured lane

utilization percentages (i.e. if more cars utilize a certain lane of a dual left turn movement over

the other lane; this lowers capacity), measured signal timings for each phase, measured peak

hour factors, etc.. In order to be accurate, they should not be estimated with default values.

Calculation results should accurately reflect observations in the field of traffic conditions, for each

intersection approach. A micro-simulation model will enable this to be done visually on a

computer, as it shows an animation of traffic flows and turning movements based on real signal

timings that can easily be compared to real world conditions in the field. They show queues and

conflicts and traffic blocking traffic, etc. Once calibrated, project and cumulative traffic volumes

can be added to it to consider results of future scenarios.

Data Assumptions: Saturation Flow Rate (SFR) Factor2, Signal Timing, and Lane Utilization. The

default SFR value of 1900 cars per hour per approach lane was used in the Belvedere Place traffic

study, but Traffic Works’ field observations and measurements of pm peak hour traffic on a

Tuesday between 4 and 5 pm indicated that this SFR value at the interchange is much lower,

fluctuating between 1450 and 1900 vehicles per hour per lane, depending on the signal cycle.

We took many measurements of SR 131 and Redwood Highway Frontage Road approach traffic,

and settled on an average of 1700 vph for the intersection saturation flow rate. This rate reflects

2 Saturation Flow Rate maybe derived from the steady state headway, which is defined as the average elapsed time between the passage of successive vehicles over the stop line in the same lane. The Highway Capacity Manual suggests recording the time of passage of the fourth and 10 vehicles over several cycles to determine this time value for 6 vehicles. This assumes that the initial queue at the start of green is at least 10 vehicles long. The first three vehicles in the queue of 10 are omitted because of start up speeds. The saturation flow is calculated by 3600 / [(t(10) – t(4)) / 6]


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a much lower capacity situation because of driver behavior (more cautious and longer headways

between vehicles, greater distance between free-flow moving cars), and intersection geometry

in the area (tight curves), especially the curvature on the NB Approach of Redwood Highway

Frontage Road The result of using an incorrect value for saturation flow rate can easily be the

difference between reporting LOS C (using SFR 1900 and 100 sec signal cycle) versus LOS D/E

(using the actual SFR 1700 with a 150 sec signal cycle) for the same traffic volumes. This is the

“traffic operations” part of the equation. When we ran the calculations for level of service using

the traffic operations features of the SynchroPro software for the intersection of SR 131 /

Redwood Highway Frontage Road (using our measured SFR of 1700 vph), the average

intersection delay was 54.5 secs/veh and was LOS D/E without the project (LOS D maximum delay

is 55 secs3, so this is right on the border of LOS E). When the project traffic was added in using

trip distribution assumptions from the study, this delay jumped to 56.9 or LOS E conditions,

breaking the CEQA significance threshold laid out in the County’s EIR standard for significance.

From the Marin County EIR Guidelines Appendix N it states that if the addition of project traffic

results in an unacceptable service level (e.g. below LOS D), then it “significantly impacts” the

intersection.

Direct Comparison Analysis of Level of Service. The latest version of the Belvedere Place traffic

study used recently taken 2015 traffic turning movement count data in the most recent study

update analysis, but still used a 100 second signal cycle value in all calculations at this location

and using a 1900 vph saturation flow rate per lane yielding an LOS C result with 28.8 secs average

delay, which was not accurate. Using the traffic study turning movements “as is”, our level of

service analysis findings for this intersection were much different using additional critical data in

the calculations. We used a 150 signal cycle length (actual field measurement) and a 1700 vph

saturation flow rate (actual average field measurement) with 60% lane utilization of the inside

NBL movement (actual field measurement). The SynchroPro analysis software yielded LOS D/E

conditions with 54.5 secs average delay for the same volumes of intersection traffic. The NB

approach level of service for Redwood Highway Frontage Road at SR 131 was LOS F conditions,

with an average delay of 115.6 seconds per vehicle, an LOS F condition far higher than the

beginning of LOS F at 80 seconds average delay. At LOS F drivers will wait through more than one

signal cycle on the average. This represents the existing condition, which we also experienced in

personally driving through the intersection during the pm peak hour.

Direct Comparison Analysis of Queueing. Our field measurements of the number of cars queued

for the Redwood Highway Frontage Road NB approach on Tuesday October 27, 2015 from 4 to 5

pm was between 25 to 30 vehicles, sometimes backed all the way down to Reed Road, a distance

of 850 feet. This direct field measurement using video is in contrast to the software “estimated”

queue length of 14 cars found in Table 9 of the traffic study for the pm peak hour. The reason

for the difference is because an LOS C condition was used in the study instead of the actual LOS

3 See Table 1, Intersection Level of Service Criteria, Belvedere Place Traffic and Parking Study, June 24, 2015


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D/E condition based on measured saturation flow rates, the correct signal cycle length, and

proper lane utilization percentages and signal timings.

CONCLUSIONS

More Data are Needed. Operations Analysis Needed The Belvedere Place Traffic and

Parking Study requires additional traffic operations level analysis to properly address the

existing traffic levels of service, and the resulting impacts of the project onto the existing

system. Without this level of analysis it is impossible to relate the analysis results to real

world condition traffic operations. The “planning level” analysis used does not take into

consideration specific traffic operations related to intersection geometry (i.e. sharp

turns), saturation flow rates (based on driver behavior headways and road conditions),

actual signal timing and cycle lengths (which significantly affect LOS), as well as peak hour

factors (PHF) by approach lane. Once the baseline traffic operations are analyzed based

on a higher level of field measurements, and is calibrated, validated, and vetted by

agencies such as Caltrans, etc., then it is ready to use as a foundation for analyzing the

project and cumulative impacts.

Trip Distribution. The trip distribution assumptions have also been called into question

by the City of Mill Valley, with suggestions that more of the traffic should have been

assigned to the north on US 101 freeway. While it would be ideal if all jurisdictions agreed

on trip distribution assumptions for a project, it is not a requirement for a traffic study

and in some cases probably not achievable for many projects. Traffic Works is not in a

position to determine the “correctness” of the trip distribution assumption. The W-Trans

report states that the trip distribution pattern was based on the “ratios of turning

movements at the various study intersections.” This needs clarification. It is not clear how

this was done or which intersections were used as a basis. Our cursory review of existing

pm peak traffic flows along the Redwood Highway Frontage Road serving various

development in the vicinity of the project site shows that traffic volumes along the

corridor are higher on the north end near SR 131 than they are on the south end at De

Silva Island Dr. (500 vph leaving Redwood Frontage at SR 131 and only 344 vph going

southbound at De Silva Island Dr., indicating that more drivers in the vicinity are headed

to and from the north than south). Some of the methods used in developing trip

distribution include 1) using traffic turning movement patterns at intersections as a guide,

2) use of a traffic model to determine regional patterns, 3) professional judgment.

Perhaps a better method would be to look at trip distribution directly to and from

Belvedere Place at Belvedere Drive to see where the general office traffic is currently

headed, and especially when it gets to the frontage road. Does it turn northbound or

southbound? Trip Distribution assumptions and methodology should be agreed upon in

advance between government agencies including Caltrans in order to be adequate and

defensible in the CEQA process, because they can significantly affect the outcome of the

analysis. If the pattern was to be “flip flopped” as suggested by the City of Mill Valley,


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then the traffic volumes for the project could easily double their impacts at the SR 131 /

US 101 interchange with a much different result.

Traffic Study Needs to be Expanded and Revised. The traffic study in its current form is

not complete or ready for the CEQA review process. There are too many unanswered

questions. This is because there are significant omissions from the traffic study scope

based on guidelines defined by government agencies including Caltrans. The study should

have an operations level analysis with micro-simulation to adequately address the traffic

situation at the Caltrans interchange facilities, specifically at the US 101 and SR 131

interchange where four closely spaced intersections are operating at congested

conditions with very long signal cycles, with some side street approaches at LOS F+

conditions for over 500 vehicles an hour in the peak (the average delay for each: 115.6

secs/veh). Additional intersections would need to be added to the analysis to include SR

131 and US 101 coordinated signalized intersections, also as per Caltrans guidelines. In

addition, Caltrans had recommended that the intersection of Belvedere Dr. and E.

Strawberry Dr. be added because of its close proximity (within 60 feet) and influence on

the SR 131 / E. Strawberry Dr. signalized intersection. We concur.


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ITEMIZED REVIEW PROCESS: LETTERS and COMMENTS

This section details our specific peer review of reports, letters, and reference documents, etc., in

a point by point analysis. Items appear here in the in order of the outlined scope of work

developed by the County.

SECTION I: The following documents were reviewed for accuracy and completeness in

evaluating the proposed project for traffic impacts both for direct and cumulative impacts.

1. W-Trans Belvedere Place Traffic and Parking Study dated October 23, 2014

Assessment: Study has some inaccuracies and an incomplete scope of work. This initial

W-Trans traffic study for Belvedere Place only examined three intersections and used

generalized default assumptions for capacity analysis pertaining to saturation flow rates,

signal timing, cycle lengths, etc. It was later determined through public hearings and

government agency input that additional intersections were needed in the study, and the

scope of work expanded. We reviewed the initial traffic study and agree with several of

the comments raised, that the study scope of intersection locations needed to include the

Caltrans US 101 / SR 131 interchange intersections as per Caltrans guidelines, since they

are interconnected and coordinated and work as a system of four intersections, closely

spaced, and directly impacted by project traffic. Traffic Works measured saturation flow

for SR 131 EB approach as well as the Redwood Highway Frontage Road northbound

approach. The measured saturation flow rates varied from 1,440 vph to 1,900 vph,

averaging around 1700 vph/lane. The NB approach has a sharp curve slowing traffic

speeds slightly, and the LOS is very poor in the pm peak hour, causing drivers to wait 2 or

sometimes 3 signal cycles to get through. This LOS F condition for the short 38 second

phase timing for NB approach was not identified in the W-Trans report, but the

intersection as a whole was reported as LOS C average delay of 24.7, with a NB approach

LOS D and 46.7 secs of delay. This calculation does not match the existing condition

calculated by Traffic Works where the NB approach has LOS F conditions with nearly two

minutes of average delay per vehicle (nearly three times higher), and an overall

intersection LOS D/E condition with 54.5 secs average delay for the intersection. The W-

Trans report did not use measured saturation flow rates, did not use the actual signal

timings or cycle length, and did not factor in lane utilization for the dual left turn lane

imbalance. These omissions led to an inaccurate level of service calculation at this critical

intersection, which must be revised.

The study scope of work should have been prepared with input from local government

agencies, including Caltrans, and all Caltrans and adjacent intersections affected by

project traffic flows should have been included in the report scope. The trip distribution

should be fully explained and developed with approval from local government agencies,

as it significantly affects capacity calculations when the volumes change.


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2. March 10, 2015 Letter from Bruce Corcoran

Are all issues raised in this letter addressed adequately?

Assessment: Yes and No. The letter raises several issues about the original Oct. 23, 2014

W-Trans traffic study including: 1) The vacancy in the Belvedere Place office complex is at

best 80% and therefore traffic counts in the area are less than they would be if it were at

100% occupancy. 2) The planned SB left turn pocket intersection improvements to

Redwood Highway Frontage Road at the US 101 NB ramps intersection (with De Silva

Island Drive) were used in the analysis, and should not have been since they do not yet

exist. 3) The study should also analyze Redwood Frontage Road at Seminary Drive as well

as at Reed Blvd. Also Belvedere at Reed and Belvedere and Tiburon Blvd. 4) The traffic

counts were taken in December 3, 2013 on a Tuesday, and are out of date. Also that

Tuesday traffic is light. 5) Mid-day peak hour counts were not taken and included in the

study. 6) The calculated LOS in the W-Trans of LOS C or better does not comport with

other traffic studies reporting LOS D, E, and F conditions. The appendix shows LOS E and

F for various approach lanes but averages all lanes to give a more favorable intersection

average LOS.

The revised W-Trans traffic study did address each of the issues raised in this letter by 1)

adding to existing traffic counts that portion of the office building traffic that would

generate if it were at 100% occupancy, 2) The planned SBL pocket protected phasing

future improvement was eliminated from the existing conditions analysis, 3) the

additional four intersections mentioned were added to the study scope, 4) new traffic

counts were taken in 2015 shortly after this letter, 5) a mid-day peak hour analysis was

included in report along with new mid-day traffic count data, and 6) but the study

continued to report LOS C conditions at the critical intersection of SR 131 and Redwood

Frontage Road because of the planning level methodology used to calculate level of

service. However, it is industry standard practice to report the intersection average LOS

and average delay overall. It is still possible to discuss various intersection approaches in

a traffic study where traffic operations are very poor, something the W-Trans study did

not do for the NB Redwood Frontage approach at SR 131.

3. W-Trans Belvedere Place Traffic and Parking Study dated June 24, 2015

Assessment: Study still has some inaccuracies and an incomplete scope of work. The

level of service calculation methodology used in the W-Trans report is still a “planning

level” calculation and not the “traffic operations” level that is needed for the existing

near-capacity conditions that exist at the US 101 / SR 131 interchange intersection

system. Much anecdotal information has been presented by Caltrans and local

Strawberry residents concerning the level of service conditions at SR 131 and Redwood

Frontage Road, that LOS F conditions exist for the NB approach and LOS D/E conditions

exist as an overall average for the intersection. Traffic Works has conducted traffic


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counts, measured timing of phasing and signal cycle lengths, measured saturation flow

rates for SR 131 and for Redwood Frontage Road, in an effort to nail down the

representative level of service and queue lengths that match what we observed in the

field. We also took video to capture and study the traffic volumes and flows and

determine saturation flow rates, etc. Our assessment of traffic operations at this location

is that LOS F+ conditions exist for the NB approach (80 seconds of delay is when LOS F

begins, and this approach currently is at 115.6 seconds of delay per vehicle, average).

Adding more traffic to this condition becomes a significant impact. The Marin Countywide

Plan Update Final EIR, November 2007 identified this location as operating at LOS F

conditions. The traffic levels on US 101 have not changed much in the past 8 years, and

in fact have slightly increased from 2007 to 2014 as is shown in the following excerpt from

the Caltrans Traffic Count data obtained from their website4.

Caltrans Traffic Count Data for Year 2014 and 2007

Year 2014 Caltrans peak hour freeway totals in study area. Note the volumes at JCT. RTE. 131 EAST show 10800 cars before this interchange and 14000 cars after.

Note that the Year 2007 volumes are 10600 and 13400 for JCT. RTE. 131 EAST

This traffic count record shows that traffic volumes overall have increased on US 101 since

2007, and that the level of service reported for this intersection by the Marin Countywide

Plan Update Final EIR, November 2007 was relevant, and that traffic counts in the area

for 2015 are not lower yielding better levels of service (such as LOS C). In fact, Caltrans

traffic levels at the US 101 interchange with SR 131 for Year 2014 are very similar to the

Year 2007.

4. Caltrans Letter dated July 14, 2015

Assessment: This Caltrans letter was generated after the final study of Belvedere Place,

raises some issues with the study, but the issues were explained away in a response

letter by W-Trans without updating or making the Caltrans recommended changes to

4 http://traffic-counts.dot.ca.gov/

http://traffic-counts.dot.ca.gov/


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the report. The issues raised by Caltrans concerning the contents of the traffic study

included:

Highway Operations

1) The LOS at the intersection of SR 131 and Redwood Frontage Road would be worse

than shown in the traffic study (LOS C), and should be re-evaluated with the existing

queuing delays considered.

2) The operations of traffic at the SR 131 / Redwood Frontage intersection would be worse

than what the W-Trans report shows.

The operations at the SR 131/Redwood Highway Frontage Road would adversely impact

the US 101/SR 131 interchange. The study should include the freeway ramp signalized

intersections.

Traffic Works concurs with these concerns by Caltrans, that the operations of the SR 131

and Redwood Frontage Road intersection is worse than LOS C shown in the report, and

should be reevaluated using accurate traffic operations data such as calibrated saturation

flow rates, actual signal timings and phasings, actual signal cycle timing, etc.

We agree that the US 101/SR 131 freeway interchange intersections could be affected by

traffic from the operations of the SR 131/Redwood Frontage Road intersection. For this

reason, the interchange ramp intersections need to be a part of the study scope to

determine impacts to the interchange, since they work now as a coordinated system.

Traffic Safety

Caltrans recommended that the study scope be increased to add the intersection of E.

Strawberry and Belvedere because it is so closely spaced to the study intersection of SR

131 (Tiburon Blvd.) and E. Strawberry Dr. (only 60 feet between Tiburon Blvd. and

Belvedere Dr.). Traffic Works conducted an independent review of am peak hour traffic

conditions at this intersection using SynchroPro 9 and calculated LOS D conditions with

queues for northbound E. Strawberry Dr. traffic exceeding 200 feet back from stop bar at

SR 131 (in other words, a traffic queue extending back beyond the Belvedere Dr.

intersection). The existing peak hour traffic volumes on northbound E. Strawberry Dr.

require over 200 feet of storage length in the am peak hour, but there is only 60 feet of

storage distance available. Because of this, the traffic operations of the intersection are

linked with the left turn traffic movements from Belvedere Dr. trying to “cut in” to this

constant queue of traffic during peak hours. It presents a traffic operations problem that

has been partially solved by the “KEEP CLEAR” pavement marking for northbound

Strawberry Dr. at the intersection with Belvedere Dr., but this pavement marking is in the

middle of the “storage” area for northbound left turns at the SR 101 intersection, so it

can be confusing who has the right of way as there is no STOP marking for northbound


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Strawberry Dr. In other words, it warrants a closer look at the operations here at these

two closely spaced and inter-connected intersections. W-Trans did respond by stating

that there was one accident in the past 5 years at Belvedere and E. Strawberry Dr., and

that in their view the additional project traffic would not change operations. Also that

one potential mitigation of this existing condition would be to prohibit left turns out from

Belvedere. We concur with Caltrans that the traffic study should address/discuss the

mitigation of any traffic it may add in this left turn movement from Belvedere Dr. which

may also involve an expanded signal operation as a solution.

The W-Trans response letter did address the concern of Caltrans regarding the WB left

turn queue distance on SR 131 to southbound Strawberry Dr., and that there would be

no appreciable increase to queue lengths from the project. However, our calculations

using SynchroPro for the intersection showed that the 95th percentile queue length

reported would increase from 179 feet to 208 feet with the addition of 15 more cars in

the am peak hour (from 47.5k project). Since the left turn pocket is only about 180 feet

from beginning of taper to stop bar, this is currently at the edge of queue length capacity.

Caltrans also encouraged a Travel Demand Management (TDM) program for the County,

and the W-Trans report did address this by recommending that the project tenants

develop and submit to the County a TDM program to help reduce employee related trips

during the peak hour time periods.

5. W-Trans response to Caltrans Comments dated July 27, 2015

Are issues raised by Caltrans addressed adequately?

Assessment: The response letter by W-Trans RE Caltrans concerns did not adequately

address the overarching Caltrans concerns relating to US 101/SR 131 interchange

operations and impacts. Ms. Patricia Maurice, Branch Chief, Local Development –

Intergovernmental Review at Caltrans District 4, raised several questions about the traffic

study in a letter to Marin County’s Scott Greeley, and these questions are outlined in the

response letter by W-Trans sent to Bently Holdings (applicant). The first question by

Caltrans had to do with the level of service calculation at the intersection of SR 131 and

Redwood Highway Frontage Road. Caltrans said that the actual level of service would be

worse than the LOS C condition shown in the W-Trans report because queuing delays

need to be taken into consideration. Caltrans said that the intersection should be

reevaluated. W-Trans responded that they had used a default 100 second signal cycle

length rather than the PASS5 recommended value of 140 seconds. Traffic Works did

measure the actual cycle length in the field with video on Tuesday October 27, 2015

during the pm peak hour, and it was 150 seconds. W-Trans did examine a calculation

using a cycle length of 140 seconds and reported that LOS D was the result with 35.8

5 Program for Arterial Synchronization (PASS), City of Mill Valley, CA


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seconds of delay, and that if the project traffic is added in the delay would only increase

a maximum of half a second, with no changes to any intersection levels of service.

Traffic Works conducted an independent level of service calculation for the SR 131 and

Redwood Frontage Road intersection, but using the same W-Trans traffic turning

movement counts, and got a much different result. This is because we conducted an

“operations based” traffic analysis that took into consideration the traffic queues Caltrans

mentioned, as well as accurate saturation flow rates. We observed much longer queue

lengths for the NB approach in the field nearing 30 vehicles instead of the TRAFFIX

software estimated 14 cars reported in Table 9 of the W-Trans report. We also measured

several saturation flow rates at this intersection directly during the pm peak hour in the

field. We measured the signal phasing timings and signal cycle length (was 150 seconds),

as well as the specific lane utilization for the NB dual left turn approach (was only 60% for

inside lane). These factors are influenced by driver behavior, intersection shape and

geometry, and therefore also affect the calculated level of service. The result of our

analysis was borderline LOS D/E conditions for the pm peak hour with an average delay

overall of 54.5 secs/vehicle (at 55 seconds it changes to LOS E). This compares to the

more limited “planning level” analysis conducted by W-Trans which yielded a calculated

LOS D using the 140 second cycle length and a stated 35.8 secs of delay. This significant

difference in results is directly related to a lack of data in the W-Trans report, as well as

overlooking several important key factors for the intersection traffic operations including

using a measured saturation flow rate, using the correct signal timing and cycle length,

using the correct lane utilization, etc.

Since this intersection is included as a part of four coordinated signal operations on SR

131 at the US 101 freeway ramps, it is important that this key intersection at Redwood

Frontage Road be calculated properly, and that a micro-simulation model be used to

identify any operational problems not addressed by the TRAFFIX software.

6. Mill Valley Letter dated July 30, 2015

Specifically whether all points raised in the “Review of Traffic Study” section were

correctly analyzed

Assessment: The Mill Valley letter to the Board of Supervisors identified several issues

with the traffic study analysis, with which we concur as explained below. In the “review

of traffic study “section the City listed the following items as needing to be done for the

study:

1) New intersections should be added at Tiburon Blvd/East Blithedale Ave, US 101 SB

Off-ramp, and US 101 NB Off-ramp. We concur, since these three intersections are part

of a four intersection coordinated system of intersections at the US 101/SR 131

interchange. The SR 131/Redwood Frontage Rd intersection is the fourth intersection.


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These should be studied as a group of intersections in a micro-simulation model to check

for queuing and blocking problems. It can be used to double check the static single

intersection analysis conducted in software such as TRAFFIX or SYNCHRO, and to help

identify operational problems which should be discussed at this location, since many do

now exist (i.e. NB approach of Redwood Frontage at SR 131).

2) Correct LOS at Frontage intersection. We concur. The intersection LOS at this location

should be LOS D/E when using proper saturation flow rates, signal timings, and lane

utilization reflecting actual conditions.

3) Analyze queuing impacts throughout the East Blithedale Ave corridor. Depends on

trip distribution of the project traffic. We agree that the four intersections at the US 101

interchange should be included in the study, but have no opinion on whether Mill Valley

intersections to the west beyond the interchange “group of four” intersections should be

included. This is a decision that needs a more compelling reason to implement expanding

the scope of work into the City of Mill Valley along the E. Blythedale corridor to the west

of US 101. We don’t see the need with the information we have available to us.

4) Evaluate Year 2035 conditions. Typically a cumulative analysis is needed if the project

traffic will in any way contribute to impacts to future traffic. In this case, it will be needed

because traffic volumes continue to grow in this congested area as shown by Caltrans

traffic count data increasing on US 101 over the past decade.

5) Fix Trip Distribution flip flopped assumptions for US 101 as traffic demands are to

and from the north primarily, When examining the volumes of traffic that leave vicinity

of the project site along Redwood Frontage Road, it can be seen that the majority of traffic

exits at the intersection with SR 131 (500+ vph through NB approach), vs. the 315 vph

going south on Redwood Frontage at De Silva Island Dr. some of which may enter the

freeway to go south. We concur that the trip distribution assigned to the north on US 101

is low when compared to outgoing existing volumes of traffic.

7. ITERIS City of Mill Valley / Caltrans / MTC Program for Arterial System Synchronization (PASS)

FY 13/14

Assessment: The ITERIS report conclusions for SR 131 were not utilized in the analysis

assumptions made throughout the W-Trans report scenarios. The ITERIS report

communicates that the City of Mill Valley currently operates signal coordination at

intersections along East Blithedale Ave during am and pm peak hours, and that new

recommended timings will be implemented in May of 2014. . This report recommended

that the intersection of SR131 (Tiburon Rd) at Redwood Highway Frontage Road have a

signal cycle length of 140 seconds (see Table 2, Proposed Cycle Length Values), as well as

the US 101 NB Off-ramp intersection. The W-Trans study did acknowledge knowing of

this longer cycle length in a response letter to the applicant, but did not incorporate it


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into report analysis or appendix. The appendix still shows all revised calculations using a

100 second cycle length for this intersection. In addition, the traffic report did not use

actual saturation flow rates or signal cycle lengths or signal phasing timings that are in

play at this intersection.

8. August 10, 2015 Letter from Bruce Corcoran


Assessment: The letter identifies several questions arising from a reading of the traffic study

that need further clarifications.

The first point raised in the letter is that the project will add an additional 627 to 1192 trips

per day but the study communicates that there would be no significant impact to an already

congested system. Our response is that the impact of a project depends on where the traffic

will go. The trip distribution pattern of the project sends project traffic to various locations

according to the assumptions of that trip distribution. The City of Mill Valley has called into

question the assumptions for the trip distribution pattern saying they’re too low for the SR

131/Redwood Highway intersection, so this could change in an updated traffic study. Also,

our independent traffic operations analysis of the SR 131/Redwood Frontage intersection

show that the actual traffic operations level of service overall for the intersection is LOS D/E,

and not LOS C as reported in the traffic study for the pm peak hour. This is because the traffic

study conducted a traffic planning analysis with less data when a traffic operations analysis

was more appropriate because of known traffic operational issues at this intersection, and

because it is linked to a Caltrans interchange facility by signal coordination. Because the

intersection overall is at LOS D/E conditions, almost any level of traffic added will be a

significant impact, because of the policy of the Marin County EIR Guidelines, Appendix N,

Criteria for Significance, which states that it is significant if LOS D is exceeded. The addition of

project will cause LOS E conditions when added to existing traffic volumes.

Other items brought to attention in this letter include the level of service at SR 131/Redwood

Frontage Road not being at LOS C as stated in the report. We concur with that point as it

should be LOS D/E. In addition the Marin Countywide Plan is stated as having indicated this

location being at LOS F conditions, and we concur because the same report also stipulates

that major and significant improvements are planned for this US 101 interchange

including bridge widening to add more lanes to increase capacity. This is because of the

projected growth of traffic.

9. Six emails from Mark Leiberman dated October 7, July 9, July 10, June 25, March 10 (2), 2015


The main issues raised in the letter have to do with traffic calming requests for Belvedere

Drive, and the effects of traffic on pedestrian safety. It is recommended that the study

address these issues and provide appropriate mitigation suggestions for the street, which


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may or may not be directly related to the project (since they are existing conditions

identified in the letter).

SECTION II: Conclusions shall be clearly rendered regarding the following:

1. In the consultant’s professional opinion, do the studies substantially conform to the 2007

Marin Countywide Plan Transportation Section 3.9?

No. The 2007 Marin Countywide Plan identifies the US 101 interchange with SR 131 as in need of major improvements in the future, because levels of service below LOS D conditions will exist in the future. Reference is made to the Marin Countywide Plan 3.9 Transportation Map 3-6b. We have included that map as Figure 1 for reference. In that figure it shows the extent and location of various future improvements, and the improvements listed for the US 101 / SR 131 interchange (Locations 16 and 17) as follows:

16. Improve Tiburon Blvd. overcrossing with additional lanes (particularly in the eastbound direction from southbound U.S. 101 to Strawberry Dr.), more off-ramp and on-ramp capacity, accommodation of bicyclists and pedestrians, and better access to bus transit stops in the interchange. 17. Widen southbound U.S. 101 off-ramp at Tiburon Blvd. /East Blithedale and improve the traffic distribution at the ramp terminus with East Blithedale.

These major improvements called for in the Marin Countywide Plan are based on traffic levels falling

below the LOS E threshold for freeways and LOS D threshold set for all other surface street roads in

the County.

The traffic study analysis needs to be modified to be sensitive to the projected LOS F conditions for

the US 101 freeway and its interchange with SR 131 overcrossing bridge, which is slated for widening.

The project’s impacts need to be analyzed for conditions leading up to that time of mitigation, and

possibly with the additional impacts the cumulative traffic growth will also bring.


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Figure 1 Map 3-6B from Marin Countywide Plan, Section 3.9 Transportation


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2. According to CEQA Appendix G: Environmental Checklist Form Section XVI. Transportation /

Traffic and the Marin County EIR Guidelines, Appendix N, Criteria for Significance, could the

project result in any Potentially Significant Impacts related to traffic?

From the Marin County EIR Guidelines Appendix N the following questions exist and we

have answered them accordingly:

Does the project traffic significantly impact intersection LOS resulting in an

unacceptable service level (e.g. below LOS D)? In the case of the SR 131 / Redwood

Highway Frontage Rd. intersection, the answer is yes, the project does have a significant

impact on intersection LOS. The resulting level of service is LOS E with the project traffic

added in, and especially if the trip distribution pattern is adjusted to the more realistic

pattern of sending more traffic to and from the north through the US 101 / SR 131

interchange ramps.

Does the project have adequate parking and internal circulation capacity to

accommodate projected traffic so that off-site areas are not adversely affected? Yes.

We have examined the details of Table 10 of the traffic study as well as the parking

discussion and find that the site has adequate parking available even if 47,500 SQFT of

the 100,000 SQFT of general office is converted to medical office. Currently there are 400

spaces available and only 348 are needed with the proposed project for all uses at the

site.

Does the project include provisions for pedestrian and bicycle circulation and bicycle and

motorcycle parking and security? The traffic study does not address these alternative

modes of bicycle or pedestrian traffic to and from the project site, nor does it address

motorcycle parking and security.

3. In the consultant’s professional opinion, were the studies conducted in conformance with

industry standards?

Generally yes. Traffic study scope and considerations often depend on the client,

available budget, who developed the scope of work and the purpose/goals of the study.

These are factors that are unknown to us reviewing the traffic study. What we do know

from watching the on-line recordings of the BOS meetings relating to this project

application is that the project applicant developed through analysis a project description

that would avoid significant traffic

impacts (avoid the LOS D/E impact

threshold). Sometimes the traffic is

complicated and cannot be

adequately described or analyzed

using “planning level” analysis

methodology as was discovered at

Figure 2 From “Map 3-6b” Proposed Major Transportation Improvements planned at US 101 / SR 131 interchange. …from Marin Countywide Plan 3.9 Transportation Section


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the SR 131/Redwood Frontage intersection. The methods used to analyze traffic were in

conformance with industry standards for a “planning level” study. However the traffic

conditions in the vicinity of the project especially at SR 131 and Redwood Frontage Road

and the adjacent interchange intersections will undergo significant widening including

freeway overpass widening in the future as outlined in the Marin Countywide Plan 3.9

Transportation Map 3-6b. Several extant traffic studies including ITERIS, PASS, and the

Marin Countywide Plan, etc. show that this interchange location is operating poorly and

will require major improvements in the future6, which usually dictates that a “traffic

operations” level of analysis will be necessary to properly analyze traffic conditions. It is

beyond a planning level analysis at this point when LOS D conditions already exist

(saturated flows). The ITERIS report and City of Mill Valley indicated that specific signal

coordination in timing of phases for multiple intersections was going to be implemented

along the SR 131 corridor including the interchange. This has already taking place nearly

a year before the W-Trans traffic study was finalized, so it should have been included.

4. In the consultant’s professional opinion, do the studies substantially conform to the 2002

Caltrans Guide for the Preparation of Traffic Impact Studies?

No. In that document it specifically states that the scope of work is to be developed in

coordination with input from lead government agencies including Caltrans, and that all

Caltrans facilities (intersections) that would be impacted by project traffic must be

included in the scope of work to determine significance. Since the US 101 / SR 131

interchange and ramp intersections were omitted from the study, it cannot be said that

the study substantially conforms to the 2002 Caltrans Guide for the Preparation of Traffic

Studies. Caltrans requires a traffic study even when a project generates any amount of

traffic if local Caltrans facilities are experiencing LOS E or F.

The Caltrans document also says:

“When a proposed project is seeking specific entitlements (i.e., site plans,

conditional use permits, sub-division, rezoning, etc.), the following scenarios must

be analyzed in the TIS:

a) Existing Conditions - Current year traffic volumes and peak hour LOS analysis of

effected State highway facilities. b) Proposed Project Only - Trip generation,

distribution, and assignment in the year the project is anticipated to complete

construction.

6 On Map 3-6b of the Marin Countywide Plan it shows that at location 16 and 17 major improvements to the US 101 / SR 131 interchange are proposed. The Tiburon Blvd overcrossing will have additional lanes (widen the bridge) especially in the eastbound direction from the SB Off-ramp all the way to Strawberry Road. It also says more capacity must be added to the freeway on and off-ramps, accommodate bicyclists and pedestrians, and have better access to bus stops in the interchange.


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c) Cumulative Conditions (Existing Conditions Plus Other Approved and Pending

Projects Without Proposed Project) - Trip assignment and peak hour LOS analysis

in the year the project is anticipated to complete construction.

d) Cumulative Conditions Plus Proposed Project (Existing Conditions Plus Other

Approved and Pending Projects Plus Proposed Project) - Trip assignment and peak

hour LOS analysis in the year the project is anticipated to complete construction.

e) Cumulative Conditions Plus Proposed Phases (Interim Years) - Trip assignment

and peak hour LOS analysis in the years the project phases are anticipated to

complete construction.

The Belvedere Place Traffic and Parking Study did not include future cumulative scenarios,

but would have been required to according to Caltrans traffic study guidelines given the

magnitude of traffic from the project and the impact to state facilities.

5. List of inadequacies, if any, and tasks recommended to make the traffic and parking study,

from the applicant, adequate and complete.

In summary from the discussions above, the following is a list of the tasks recommended

to make the traffic and parking study adequate and complete:

1. Expand the scope of work.

a. Add Intersections. Include the US 101 freeway ramp intersections as well

as the City of Mill Valley intersection to the west of the US 101 SB off-ramp.

Also include the intersection of Belvedere Dr. at E. Strawberry Dr. as a new

intersection coupled with the SR 131 / E. Strawberry Dr. intersection

(which already exists in the report).

b. Use Micro-simulation. Use a calibrated and validated micro-simulation

model to analyze the four adjacent intersections at the US 101 freeway

interchange with SR 131. This tool will enable examination of queues and

operations for specific signal timings between coordinated intersections.

c. Include Cumulative Scenarios. Include all of the scenarios identified in the

2002 Caltrans Guide for the Preparation of Traffic Impact Studies , as listed

in Item 4 above (cumulative scenarios needed, approved projects, etc.).

d. Use Traffic Operations Analysis. Analyze signalized intersections with

“traffic operations” data input including measured saturation flow rates,

lane utilization, peak hour factors, actual signal timings and cycle lengths,

etc.

e. Clarify and possibly modify Trip Distribution Pattern. Consult with local

government agencies to develop a trip distribution pattern that is

agreeable to all parties involved (consensus), based on reasonable

assumptions.


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If you have any questions about this report, please do not hesitate to ask.

Sincerely, TRAFFIC WORKS, LLC

Grant P. Johnson, TE Principal

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