amats: mountain a rive extension

AMATS: MOUNTAIN AIR DRIVE

EXTENSION

Project No.: UAA CED 2021.02

DESIGN STUDY REPORT

ALASKA

DEPARTMENT OF TRANSPORTATION

AND PUBLIC FACILITIES

PREPARED BY: Engifar, Inc

2900 Spirit Dr

Anchorage AK 99508

April 2021

ALASKA

DEPARTMENT OF TRANSPORTATION AND PUBLIC FACILITIES

DESIGN AND ENGINEERING SERVICES – CENTRAL REGION

DESIGN STUDY REPORT

For

AMATS: Mountain Air Drive Extension

Project No.: UAA CED 2021.02

Written by: Erich Ramirez, Andrew Hwang, Shoshanna Johnson, Jasmine Langmann, Kadin

Yockey, Yamin Man

Prepared by:

__________________________________

Erich Ramirez Date

Project Engineer

Concur by:

__________________________________

Jasmine Langmann Date

Structural Lead

Concur by:

__________________________________

Andrew Hwang Date

Intersection Designer

NOTICE TO USERS

This report was created as part of a University of Alaska Anchorage Civil Engineering Department

project and reflects the thinking and design decisions at the time of publication. Changes frequently occur

during the evolution of the design process, so persons who may rely on information contained in this

document should check with the Alaska Department of Transportation and Public Facilities for the most

current design. Contact the Design Project Manager, Erich Ramirez at 907-785-25837, for this

information.

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AMATS: Mountain Air Drive Extension i Design Study Report

TABLE OF CONTENTS LIST OF FIGURES .................................................................................................................................... ii

LIST OF ACRONYMS ............................................................................................................................. iii

1.0 PROJECT DESCRIPTION ................................................................................................................. 1

1.1 Project Location and Description ...................................................................................................... 1 1.2 Existing Facilities and Land Use ...................................................................................................... 1 1.3 Purpose and Need ............................................................................................................................. 2

2.0 DESIGN STANDARDS AND GUIDELINES .................................................................................... 2

3.0 DISCUSSION OF ALTERNATIVES ................................................................................................. 3

3.1 Mountain Air Drive Alignment Alternatives .................................................................................... 3 3.2 Rabbit Creek Road / Mountain Air Drive Intersection Alternatives ................................................. 5

4.0 PREFERRED ALTERNATIVE .......................................................................................................... 8

4.1 Mountain Air Drive Preferred Alignment ......................................................................................... 8 4.2 Rabbit Creek Road / Mountain Air Drive Preferred Intersection ..................................................... 9

5.0 TYPICAL SECTIONS ......................................................................................................................... 9

6.0 HORIZONTAL AND VERTICAL ALIGNMENT ......................................................................... 10

6.1 Horizontal Alignment ..................................................................................................................... 10 6.2 Vertical Alignment .......................................................................................................................... 10

7.0 EROSION AND SEDIMENT CONTROL ....................................................................................... 10

8.0 DRAINAGE ......................................................................................................................................... 10

9.0 SOIL CONDITIONS .......................................................................................................................... 10

10.0 ACCESS CONTROL FEATURES ................................................................................................. 11

11.0 TRAFFIC ANALYSIS ...................................................................................................................... 11

12.0 SAFETY IMPROVEMENTS .......................................................................................................... 11

13.0 RIGHT-OF-WAY REQUIREMENTS ........................................................................................... 11

14.0 PEDESTRIAN AND BICYCLE FACILITIES .............................................................................. 12

15.0 UTILITY RELOCATION AND COORDINATION .................................................................... 12

16.0 PRELIMINARY WORK ZONE TRAFFIC CONTROL ............................................................. 12

16.1 Traffic Control Plan (TCP) ........................................................................................................... 13 16.2 Public Information Plan (PIP) ....................................................................................................... 13 16.3 Transportation Operations Plan (TOP) ......................................................................................... 13

17.0 STRUCTURAL SECTION AND PAVEMENT DESIGN ............................................................ 14

18.0 COST ESTIMATE ............................................................................................................................ 14

19.0 ENVIRONMENTAL COMMITMENTS AND CONSIDERATIONS ........................................ 14

20.0 BRIDGES........................................................................................................................................... 14

21.0 EXCEPTIONS TO DESIGN STANDARDS .................................................................................. 15

22.0 MAINTENANCE CONSIDERATIONS ......................................................................................... 15

23.0 ITS FEATURES ................................................................................................................................ 15

APPENDIX A Approved Design Criteria and Design Designation

APPENDIX B Typical Sections

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AMATS: Mountain Air Drive Extension ii Design Study Report

APPENDIX C 3R Analysis

APPENDIX D Traffic Analysis

APPENDIX E Material Recommendations

APPENDIX F VE Consideration

APPENDIX G Approved Environmental Document

APPENDIX H Approved Design Exceptions and Design Waivers

APPENDIX I ITS Systems Engineering Analysis

APPENDIX J Design Memos

APPENDIX K Bridge Analysis

APPENDIX L Alternative Analysis Memo

LIST OF FIGURES

Figure 1: Project Location and Vicinity Map – Courtesy of DOT&PF ....................................................... iv Figure 2: Alignment Alternatives (red box – approximate crossing locations) ............................................ 5 Figure 3: Rabbit Creek Road and Mountain Air Drive Intersection ............................................................. 6 Figure 4: Turn Lanes Example – Courtesy of USKH ................................................................................... 7 Figure 5: Roundabout Example – Courtesy of USKH .................................................................................. 8

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AMATS: Mountain Air Drive Extension iii Design Study Report

LIST OF ACRONYMS

AADT Annual Average Daily Traffic

AASHTO American Association of State Highway and Transportation Officials

AHDM Alaska Highway Drainage Manual

AMATS Anchorage Metropolitan Area Transportation Solutions

ATM Alaska Traffic Manual

ATMS Alaska Traffic Manual Supplement

BMP Best Management Practice

BVES Bear Valley Elementary School

DOT&PF Alaska Department of Transportation and Public Facilities

DOJ U.S. Department of Justice

ESCP Erosion and Sediment Control Plan

FHWA Federal Highway Administration

HMA Hot Mix Asphalt

HPCM Alaska Highway Preconstruction Manual

LOS Level of Service

MOA Municipality of Anchorage

MPH Miles per Hour

MUTCD Manual on Uniform Traffic Control Devices

PGDHS A Policy on Geometric Design of Highways and Streets

PIP Public Information Plan

PROWAG Proposed Accessibility Standards for Pedestrian Facilities in the Public Right-of-Way

RDG Roadside Design Guide

ROW Right-of-Way

SWPPP Storm Water Pollution Prevention Plan

TMP Traffic Management Plan

TOP Transportation Operations Plan

USGS United States Geological Survey

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AMATS: Mountain Air Drive Extension iv Design Study Report

Figure 1: Project Location and Vicinity Map – Courtesy of DOT&PF

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AMATS: Mountain Air Drive Extension 1 Design Study Report

1.0 PROJECT DESCRIPTION

1.1 Project Location and Description

The Alaska Department of Transportation and Public Facilities (DOT&PF), in cooperation with the

Federal Highway Administration (FHWA) and Anchorage Metropolitan Area Transportation

Solutions (AMATS), proposes to extend Mountain Air Drive from its intersection with Rabbit Creek

Road to 162nd Avenue. The project is located in Sections SW3040, SW3139, and SW3239, USGS

Topological Map Anchorage A-8 SE, Latitude 61.0812147°N, Longitude 149.751201°W, within the

Municipality of Anchorage (MOA), near Bear Valley Elementary School (BVES). See Figure 1 for

Location & Vicinity Map.

The proposed extension will connect a 450-foot segment of Mountain Air Drive that intersects with

Rabbit Creek Road in the north of the Project Area to another 2,200-foot segment of Mountain Air

Drive that intersects with Sandpiper Drive in the south.

Additional considerations include:

• Intersection improvements at Rabbit Creek Road

• Structural crossing over Little Rabbit Creek

• Separated pathways and ADA pedestrian facilities

• Roadside ditches and drainage culverts

• Guardrails, signage, and striping

• Relocating utilities

• ROW acquisition

• Vegetation clearing and grubbing

• Soil stabilization

1.2 Existing Facilities and Land Use

The existing north and south separated segments of Mountain Air Drive are two-lane Rural Collectors

with 60-feet of ROW. Both segments lack a posted speed limit, curb and gutter, pedestrian facilities,

or striping.

The north segment of Mountain Air Drive is a 450-foot-long, 36-foot-wide, paved facility, and

provides access to BVES and Anchorage Fire Department Fire Station No. 10. While the Anchorage

Hillside area is often classified as rolling or mountainous terrain, the existing northern segment of

Mountain Air Drive is relatively flat. Drainage is provided by culverts and roadside ditches. The north

segment of Mountain Air Drive ends in a cul-de-sac at the entrance to BVES. A foot trail continues

where the pavement ends and primarily follows the platted ROW of Mountain Air Drive around the

outside of BVES until it connects with the platted ROW of Hillside Drive, near the SE corner of

BVES.

The south segment of Mountain Air Drive is a 2,200-foot long, 30-foot wide, paved facility on rolling

terrain, and slopes down from its intersection with Sandpiper Drive as it snakes north until it ends at a

cul-de-sac. Drainage is provided by cross culverts and roadside ditches. For the first several hundred

feet, there are developed or in-development private properties on both sides of Mountain Air Drive,

then it is undeveloped until the cul-de-sac.

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The T-intersection with Rabbit Creek Road is stop-controlled only from Mountain Air Drive. There

are no turn lanes, medians, or traffic signals at the intersection. There is one luminaire at the

intersection, on Rabbit Creek Road across from Mountain Air Drive. Rabbit Creek Road is a

residential collector at this intersection with a posted speed of 45 mph. Currently, the intersection

experiences delays during AM and PM peak hours that coincide with the start and end of the school

day for BVES.

Land use in the project area, aside from BVES and Fire Station 10, is mostly undeveloped residential

parcels. Platted ROW for Hillside Drive, Mountain Air Drive, and 155th Avenue are located in the

vicinity. A network of community trails can be found on platted ROW. Little Rabbit Creek is located

at the bottom of a 50-foot ravine and crosses the project area draining east to west. MOA-classified

wetlands of high and moderate valuation are present and are especially clustered to the south and east

of the project area. A MOA Heritage Land Bank is to the east of the Hillside Road ROW. An MOA

Heritage Land Bank is east of the project vicinity.

Utilities in the project vicinity are underground and overhead and include electric and communication

lines from Chugach Electric Association and Alaska Communications. A transformer is just off the

foot path to the west of BVES. Hanging utilities are adjacent and parallel to the Hillside Drive ROW.

A Section Line is located just east of the Hillside Drive ROW.

1.3 Purpose and Need

The purpose and need of the AMATS: Mountain Air Drive Extension project is to address safety

concerns for the surrounding communities and to spur development in this region of Anchorage,

including providing a secondary means of egress for residents and access for emergency services.

Other considerations include improving active transportation in the community, to provide

connectivity to a large undeveloped area in SE Anchorage, and to increase circulation in the Rabbit

Creek / Goldenview area.

2.0 DESIGN STANDARDS AND GUIDELINES

Design standards and guidelines that apply to the AMATS: Mountain Air Drive are contained in the

following publications:

Standards:

• A Policy on Geometric Design of Highways and Streets (PGDHS), 6th Edition, AASHTO, 2011.

• Roadside Design Guide (RDG), 4th Edition, AASHTO, 2011.

• Alaska Highway Preconstruction Manual (HPCM), DOT&PF, 2005 as amended.

• Alaska Highway Drainage Manual (AHDM), DOT&PF, 2006.

• The Alaska Traffic Manual (ATM), consisting of the Manual on Uniform Traffic Control Devices

(MUTCD), 2009 as amended, U.S. DOT, FHWA) and the Alaska Traffic Manual Supplement

(ATMS), DOT&PF, 2016.

• ADA Standards for Transportation Facilities, DOT, 2006.

• ADA Standards for Accessible Design, DOJ, 2010.

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• Guide for the Development of Bicycle Facilities, 4th Edition, AASHTO, 2012.

• Recommended Practice for Roadway Lighting (RP-8-14), ANSI / IES, 2014.

• Highway Capacity Manual (HCM), 5th Edition, TRB, 2010.

• Design Criteria Manual (DCM), MOA, Project Management & Engineering Department, 2007

with 2018 revision.

Guidelines:

• Proposed Accessibility Standards for Pedestrian Facilities in the Public Right-of-Way

(PROWAG), U.S. Access Board, 2011.

• Guide for the Planning, Design, and Operation of Pedestrian Facilities, 1st Edition, AASHTO,

2004.

Appendix A contains the Project Design Criteria and Design Designation.

3.0 DISCUSSION OF ALTERNATIVES

Alternatives for an extension of Mountain Air Drive through the project area and intersection

improvements at Rabbit Creek Road were considered separately. Three build options were considered for

each. Beginning of Project (BOP) is the intersection of Mountain Air Drive with Rabbit Creek Road, and

End of Project (EOP) is Sandpiper Drive, beyond the cul-de-sac at the end of the southern segment of

Mountain Air Drive. BOP and EOP are labelled in Figure 2.

To review the Criteria Matrix for both the Mountain Air Drive extension and the Mountain Air Drive and

Rabbit Creek Road intersection, and a discussion of the evaluation criteria, see Alternative Memo in

Appendix L.

3.1 Mountain Air Drive Alignment Alternatives

The alignment alternatives were evaluated according to Project Costs, Future Maintenance Costs,

Environmental Impact, Mobility, Accessibility, and Public Opinion. Of the criteria, Project Costs was

given the most weight, then Mobility, given the importance of purpose and need.

Figure 2 displays the Mountain Air Drive extension alternatives from BOP to EOP.

NO BUILD

The No Build alternative would not construct a roadway connecting the existing northern and

southern segments of Mountain Air Drive. With the immediate need for egress and emergency access,

the No Build option was considered for the Mountain Air Drive extension but was rejected because it

did not meet the purpose and need for the project.

ALIGNMENT 1

This alternative is the westernmost build alternative. From BOP, it follows the existing Mountain Air

Drive, continues through the foot path on the Mountain Air Drive ROW until it reaches the border at

the SW corner of BVES property, then continues primarily south-south east through the project area.

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A 150-foot single-span bridge will cross the Little Rabbit Creek valley. After the crossing, the

alignment continues primarily between large existing drainage paths until connecting with the cul-de-

sac and continuing on the existing southern segment of Mountain Air Drive until EOP.

Alignment 1 meets purpose and need of the project by prioritizing mobility through the project area.

The alternative needs a single-span bridge but has the least length of the alternatives.

ALIGNMENT 2

This alternative is slightly east of Alignment 1. From BOP, it follows the existing Mountain Air

Drive, continues through the foot path on the Mountain Air Drive ROW, around the SW corner of

BVES, until coming to a stop-controlled intersection alongside the southern BVES property border.

The alignment then proceeds south. A multi-plate arch culvert will cross the Little Rabbit Creek

valley. After the crossing, the alignment continues southwest until connecting with the cul-de-sac and

continuing on the existing southern segment of Mountain Air Drive until EOP.

Alignment 2 meets purpose and need by providing a balance of mobility and accessibility through the

project area. The alignment has a stop-controlled intersection and has a small turning radius around

the southwest corner of BVES. The alternative needs a multi-plate arch culvert and is approximately

500 feet longer than Alignment 1.

ALIGNMENT 3

This alternative is the easternmost alternative. From BOP, it follows the existing Mountain Air Drive,

continues through the foot path on the Mountain Air Drive ROW until coming to a stop-controlled

intersection as it meets with the Hillside Drive ROW to the SE of BVES, then continues south on the

ROW. Two multi-plate arch culverts will cross Little Rabbit Creek and a tributary stream. After the

crossings, the alignment will continue south until coming to a stop-controlled intersection with the

ROW for 155th Avenue. The corridor continues west on the 155th ROW, comes to a stop-controlled

intersection, then continues due south until connecting with the cul-de-sac and continuing on the

existing southern segment of Mountain Air Drive until EOP.

Alignment 3 meets purpose and need for the project by providing connectivity through the project

area for future development. The alternative needs two multi-plate culverts, has three stop-controlled

intersections and is approximately 1,800 feet longer than Alignment 1.

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Figure 2: Alignment Alternatives (red box – approximate crossing locations)

3.2 Rabbit Creek Road / Mountain Air Drive Intersection Alternatives

Figure 3 displays an aerial of the existing intersection.

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Figure 3: Rabbit Creek Road and Mountain Air Drive Intersection

NO BUILD

The no-build alternative was considered for the intersection, but would fail to meet future capacity if

the Mountain Air Drive extension was constructed. Significant traffic delays will occur in this

intersection should the Mountain Air Drive extension be built. USKH, now Stantec, conducted a

traffic study (memorandum dated January 2011) and found that during both peak AM and PM hours,

the level of service (LOS) will be unacceptable should the extension be built. Of the LOS levels, LOS

D (approaching unstable flow) is the minimum acceptable condition for intersections per MOA

standards. Per the USKH traffic study report, the existing LOS as of September 1, 2009 was at LOS B

(stable flow). However, should the Mountain Air Drive extension be built, the intersection would

experience an LOS F (forced flow) should no improvements be done on the intersection.

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TRAFFIC SIGNAL without TURN LANES

This alternative is to install a traffic signal on Mountain Air Drive and Rabbit Creek Road without the

installation of a turn lane. The Manual on Uniform Traffic Control Devices, or MUTCD, sets nine

possible warrants for the installation of a traffic signal based on traffic studies of the intersection. In

its existing condition, the intersection of Mountain Air Drive and Rabbit Creek Road only meets one

of the warrants, which concerns peak hour volume. Meeting only one of the nine possible warrants is

not ideal in its consideration of selecting this alternative. A traffic signal would allow for an easier

and more understandable pedestrian crossing, considering the intersection is located near a school.

However, the improper usage of a traffic signal would be detrimental to the flow of traffic and causes

delays outside of the current peak traffic hours. Traffic signals are also monetarily costly, as the

maintenance for a traffic signal costs approximately $10,000 a year.

TURN LANES

This alternative is the construction of a turn lane on Mountain Air Drive and Rabbit Creek Road. The

National Cooperative Highway Research Program (NCHRP) Report 457 sets a volume threshold for

the consideration of a turn lane, which this intersection meets. A turn lane is more ideal in terms of

allowing emergency access vehicles to travel and cross at, while also providing a specific lane for

through traffic on Rabbit Creek Road. Should the turn lane not be adequate when traffic volume

increases in the future, the turn lane allows for the installation of a traffic signal to accommodate for

the increase in traffic volume. This alternative will require reallocation of its existing pavement or

widening the cross-section of the roads, resulting in additional right of way needs. Installations

necessary for a future traffic signal would need to be constructed as well, as the USKH traffic study

states the additional lanes would increase the level of service to an acceptable LOS D. Per the USKH

traffic study, the level of service with a turn lane during the peak AM hour would be an LOS F, which

is the lowest LOS. The installation of a traffic signal will be necessary along with the turn lanes due

to the peak AM hour LOS. The combination of the traffic signal and turn lanes would accrue a

significant amount of cost involved with the project.

Figure 4: Turn Lanes Example – Courtesy of USKH

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ROUNDABOUT

This alternative is the construction of a single-lane roundabout at the intersection of Rabbit Creek

Road and Mountain Air Drive. A roundabout does not require electricity or any special maintenance

like a traffic signal requires, thus having lower overall maintenance costs than the installation of a

traffic signal. Roundabouts have historically reduced the frequency and severity of crashes, as well as

reducing the delay in traffic when traffic volumes do not exceed the roundabout capacity. The

intersection of Rabbit Creek Road and Mountain Air Drive has an overall intersection grade of 1%,

which is desirable as it is less than 4% as stated in the NCHRP report 672. On February 11, 2021, the

Department of Transportation and Public Facilities conducted a public meeting with the Rabbit Creek

Community Council regarding the Mountain Air Drive extension. It was found that the public was in

favor of a roundabout. The roundabout would require an additional right of way acquisition, as the

single-lane roundabout would require an inscribed circle diameter of 90 feet to 150 feet. Roundabouts

also require the drivers to slow down for the entry of a roundabout regardless of any other vehicles

being present. Per the NCHRP report 457, roundabouts are not as conductive to serving pedestrian

and bicycle traffic.

Figure 5: Roundabout Example – Courtesy of USKH

4.0 PREFERRED ALTERNATIVE

4.1 Mountain Air Drive Preferred Alignment

Beyond addressing purpose and need, Alignment 1’s most prominent characteristic is the mobility of

the thoroughfare. Two other nearby collectors were used as comparables for the Mountain Air Drive

Extension, Goldenview Drive to the west and Clarks Road to the northeast. Both Goldenview and

Clarks primarily provide direct passage to local roads that service residential neighborhoods.

Alignment 1 meets the purpose and need of the project and scored the highest using the Evaluation

Criteria. The alignment has a comparable construction and maintenance costs with the other

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alternatives, has less environmental impact, and constructs a collector with high mobility through the

project area.

Key Alignment 1 features for the public and client include:

• Creates a highly mobile thoroughfare that directly addresses purpose and need for the project.

• Minimal environmental impact throughout the corridor.

• Difference in capital costs with Alignment 2 are expected to be minimal with fewer linear

feet of road and less structural material needed for Little Rabbit Creek crossing and fewer

utility conflicts.

• Difference in maintenance costs with Alignment 2 are expected to be minimal with fewer

linear feet of road, no intersections, and bridge maintenance only required every two years.

• Alignment 1 also avoids a major constraint for the other two alignments: the curve around the

SW corner of BVES. To fit a DOT&PF desirable radius of 550 feet, there would need to be a

property acquisition from BVES. A DOT&PF minimum radius of 380 feet does fit, but the

right side of the Mountain Air Drive corridor ROW slopes down into the Little Rabbit Creek

valley south of BVES, requiring significant fill to support the right side of the roadway for

Alignments 2 and 3.

4.2 Rabbit Creek Road / Mountain Air Drive Preferred Intersection

The preferred alternative for the improvements at the intersection of Rabbit Creek Road and

Mountain Air Drive is to construct a single-lane roundabout. The roundabout has a lower overall cost

compared to the other alternatives, a higher public opinion, and provides less delay in traffic at the

intersection. Per the USKH traffic study, the roundabout has a higher level of service than the turn

lane or the traffic signal. Should both a turn lane and traffic signal be installed, the level of service

would exceed the level of service of a roundabout slightly but would be significantly more expensive

to implement. While roundabouts require more right of way acquisition at the intersection, turn lanes

have a more longitudinal right of way impact.

5.0 TYPICAL SECTIONS

The typical section is derived from DCM Figure 1-12, a typical section for a Rural Collector, with:

• 2 11-foot lanes with 4-foot shoulders, paved, with a 2% cross-slope crowned at the roadway

centerline.

• 1-foot gravel shoulders between the paved shoulder and ditch.

• ‘V’ shaped roadside ditches, with a recoverable foreslope of 4:1 that is 14-feet wide and 3.5-feet

deep and a backslope of 2:1 that is 7-feet wide.

• 2-foot sodded shoulders between the ditches and the pedestrian facilities.

• On the east side of the roadway, a 5-foot paved pathway (1.5% cross-slope), and on the west side,

an 8-foot gravel shared-use pathway (3% cross-slope).

• Outside of the pedestrian facilities, 2-feet of spacing, then 2:1 cut and fill slopes to existing

ground.

The typical section for Mountain Air Drive was adapted for the bridge crossing over Little Rabbit Creek,

with:

• 9 bulb-tee prestressed concrete girders forming the deck.

• 2 11-foot lanes with 4-foot shoulders and a 2% cross-slope.

• 3-tube railing on both sides separating the roadway from pedestrian facilities (width of 1’-8”).

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• On the east side of the roadway, a 5’-6” paved pathway (2% cross-slope), and on the west side, an

8-foot paved pathway (2% cross-slope).

• Pedestrian railing outside of the pedestrian facilities (width of 1’-0”)

The alignment and bridge typical sections are provided in Appendix B.

6.0 HORIZONTAL AND VERTICAL ALIGNMENT

6.1 Horizontal Alignment

From BOP, the first horizontal curve, in front of Fire Station 10 (Station 1 + 20), has a radius of 210

feet, a value below the minimum value in Table 1-9 of the DCM. With the proximity of the curve to

the yield-controlled single-lane roundabout intersection preferred in Section 4.2, the radius is

acceptable.

All other horizontal curve radii from the Rabbit Creek Road intersection to the cul-de-sac on the

southern segment of Mountain Air Drive are greater than the minimum limit of 600 feet for collector

roads as displayed in Table 1-9 of the DCM.

6.2 Vertical Alignment

The profile of the new alignment will match existing segments of Mountain Air Drive at the north and

south ends of the project area. Through the undeveloped area, sag curves will be present on both sides

of the valley to come down to the Little Rabbit Creek bridge. Mountain Air Drive will be designed for

a speed of 35 mph, and profile grades for the new alignment segment will not exceed 5%. The

existing southern segment of Mountain Air Drive has grades up to 8%.

The single-span bridge over Little Rabbit Creek has a + 0.70% slope moving from north to south.

7.0 EROSION AND SEDIMENT CONTROL

Outside of scope.

8.0 DRAINAGE

Outside of scope.

9.0 SOIL CONDITIONS

A geotechnical report was developed by Shannon & Wilson, Inc. in June of 2010 for the previous

Mountain Air Drive Extension project. Eleven boreholes were drilled between February 24 to March 3,

2010, along the USKH preferred alternative, with one boring being near the Rabbit Creek Road

intersection, four to the west of BVES, and six borings (three to the north and three to the south)

investigating the soils at the Little Rabbit Creek valley, at the approximate locations for the bridge

approaches and foundations. The locations of the first five borings follow the same path as this DSR’s

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new alignment. The borings along the Little Rabbit Creek valley range from 150 to 300 feet east of the

new alignment. There were no boreholes drilled south of the 155th Avenue ROW.

The report found medium dense to very dense soils. Soils were frozen from 2 to 7 feet below ground

surface. Groundwater should be expected between 20 and 35 feet below ground surface.

The Shannon & Wilson report recommends that the project does not use native soils in any structural

section.

10.0 ACCESS CONTROL FEATURES

New access to the roadway will be managed through driveway permits and future project evaluation.

Mountain Air Drive is classified as a collector, but minimal future driveway access is anticipated.

11.0 TRAFFIC ANALYSIS

The USKH traffic study was conducted on January 12, 2011, which analyzed the alternatives for the

intersection improvements between Mountain Air Drive and Rabbit Creek Road. USKH used the

Intersection LOS (level of service) Criteria to analyze the flow of traffic at the intersection using a

projected traffic volume of 1,570 trips per day with a design year set at 2029. The improvement options

were ranked with a LOS between A and F. A single-lane roundabout was found to have a LOS B in the

AM peak hour and LOS A in the PM peak hour using the projected 2029 traffic volume. The only other

alternative that reaches the roundabout’s LOS was the combination of the traffic signal and turn lanes.

12.0 SAFETY IMPROVEMENTS

Studies have shown that roundabouts reduce the severity of crashes at an intersection. The NCHRP report

672 states that intersections allow safer merging of traffic and provides more time for drivers to correct

any mistakes due to lower vehicle speeds.

The illumination of the roundabout will use a perimeter illumination design. This design has the

illumination poles along the side of the roundabout, as opposed to installing the poles on the central

island.

With the proximity to BVES, separated pedestrian facilities will be provided on both sides of the

roadway. A paved 5-foot ADA sidewalk is to be constructed on the east side of the roadway, and a gravel

8-foot multi-use pathway will be installed on the west side.

Signage and striping will be addressed later in the design process.

13.0 RIGHT-OF-WAY REQUIREMENTS

This project will require ROW acquisitions throughout the corridor. According to the OSHP, Mountain

Air Drive is a Type 1B Neighborhood Collector, and prescribes a minimum ROW width of 70 feet. To

integrate the roadside ditches and separated pedestrian facilities, the Mountain Air Drive extension will

require a minimum of 95 feet of ROW. With the cut sections for the roadway to meet the bridge,

additional ROW will be needed at the valley crossing.

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At the Rabbit Creek Road intersection, two partial acquisitions, one from Fire Station 10 and another

from a residential parcel, will be necessary for the roundabout and to achieve sight distances. West of

BVES, a strip acquisition of approximately 40 feet is needed for Mountain Air Drive ROW. On the north

ridge of the valley at Little Rabbit Creek, two full-parcel acquisitions are necessary. South of Little Rabbit

Creek, strip acquisitions from unsubdivided parcels are required for Mountain Air Drive ROW that range

from approximately 95 to 160 feet until connecting with the cul-de-sac on the southern segment of

Mountain Air Drive.

To maintain consistency along the full Mountain Air Drive corridor, strip acquisitions of approximately

20 feet on both sides of the roadway will be needed along the southern Mountain Air Drive segment for

pedestrian facilities.

14.0 PEDESTRIAN AND BICYCLE FACILITIES

With the new alignment’s proximity to BVES, pedestrian and bicycle facilities have been designed into

Mountain Air Drive’s ROW. Starting at BOP, the east side of the road, the same side that BVES is on,

features a 5-foot paved separated sidewalk, and the west side has an 8-foot gravel separated multi-use

pathway. The pedestrian facilities are separated from the roadway by 21-foot ditches. For bicyclists, the

4-foot shoulders meet the AASHTO recommendation for bicycle facilities according to the Guide for

Development of Bicycle Facilities. A cross-slope of 1.5% is designed for the paved pathway to

accommodate wheel chair users.

Pedestrian facilities are planned for the southern segment of Mountain Air Drive, but further design work

needs to take place to integrate the pathways with existing driveways.

15.0 UTILITY RELOCATION AND COORDINATION

Utility companies with facilities in the project limits include Chugach Electric Association and Alaska

Communications. Utilities will require relocation and agreements will need to be developed, at select

locations throughout the project, to address conflicts. A transformer is located near the SW corner of

BVES and will require relocation. Underground communication cables are presumed to be under the foot

path west and south of BVES, but further investigation is necessary.

16.0 PRELIMINARY WORK ZONE TRAFFIC CONTROL

Section 1400.2 of the HPCM lists the criteria for deciding if a project is ‘significant’ for purposes of

determining the level of effort required in developing a Traffic Management Plan (TMP). Significant

projects meet either the Category 1 or Category 2 classification.

Category 1

• Project occupies a location for more than three days with either intermittent or continuous land

closures on Interstate Highways within a Transportation Management Area – CRITERIA NOT

MET

Category 2

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• Project occupies a location for more than three days with either intermittent or continuous lane

closures on arterials, expressway, or freeways with Average Annual Daily Traffic (AADT) of

30,000 or more – CRITERIA NOT MET

• Project fully closes an arterial for more than one hour at a time with no practical alternate route –

CRITERIA NOT MET

• Any other project that, alone or in combination with other concurrent projects nearby, is

anticipated to require greater than normal attention to traffic control to eliminate sustained work

zone impacts greater than what would be considered acceptable – CRITERIA MET

Therefore, the project is considered a Category 2 “Significant Project” and a full TMP, including a Traffic

Control Plan, a Public Information Plan, and a Transportation Operations Plan, must be developed.

16.1 Traffic Control Plan (TCP)

The contractor will develop a TCP during construction, to safely guide and protext the traveling

public in work zones, in accordance with the Alaska Traffic Manual (ATM) and the project

specifications. The plan will be assessed and approved by the Construction Project Engineer and

Traffic Control Engineer.

The contractor is responsible for providing advance notice to the public, including local businesses,

residents, and road travelers, of construction activities that could cause delays, detours, or affect

access to adjacent properties.

16.2 Public Information Plan (PIP)

A PIP will be developed prior to beginning construction that will specify the ways and means that the

contractor will use to inform the public of upcoming activities that will impact local stakeholders, the

roadway users and public entities. The PIP will contain measures to inform stakeholders of project

scope, expected work zone impacts, closure details, and recommended action to avoid impacts and

changing conditions during construction. Measures to distribute information include:

• Contractor’s Worksite Traffic Supervisor

• DOT&PF’s Construction Section thru the DOT&PF’s 511 system

• DOT&PF’s Navigator website

• Television, radio, and/or newspaper advertisements

• Other location-specific communication tools

16.3 Transportation Operations Plan (TOP)

No large construction projects are anticipated within the vicinity of this project site so cumulative

traffic delay impacts are not expected. If unanticipated work is ongoing concurrently with the project,

the contractor must develop a TOP that will specify coordination effects from creating undue

impediment to the traveling public.

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17.0 STRUCTURAL SECTION AND PAVEMENT DESIGN

The pavement for the existing north segment of Mountain Air Drive will be removed. The existing south

segment will remain as is south of the cul-de-sac.

For the new Mountain Air Drive alignment, the structural section and pavement design will consist of 36

inches of Selected Material, Type A, 2 inches of Aggregate Base Course, Grading D-1, 3 inches of

Asphalt Treated Base Course, and 2 inches of Hot Mix Asphalt (HMA).

The sidewalk structural section on the left side of the roadway will consist of 24 inches of Selected

Material, Type A, 4 inches of Aggregate Base Course, Grading D-1, and 2 inches of Hot Mix Asphalt.

The multi-use pathway on the right side of the roadway will consist of 24 inches of Selected Material,

Type A, and 4 inches of Aggregate Base Course, Grading D-1.

18.0 COST ESTIMATE

The project cost estimate is as follows:

Preliminary Engineering $ 200,000

Right-of-Way $ 708,120

Utility Relocation $ 500,000

Construction $ 6,873,758

Total $ 8,281,878

19.0 ENVIRONMENTAL COMMITMENTS AND CONSIDERATIONS

The proposed project does not anticipate any unusual circumstances or significant environmental impacts.

The contractor will be required to prepare and implement a SWPPP.

The contractor will be required to dispose of solid waste at a DEC approved landfill. The contractor will

be responsible for obtaining all necessary permits and clearances for materials sites, disposal sites, and

staging areas unless DOT&PF has obtained the necessary permits.

20.0 BRIDGES

The proposed Little Rabbit Creek crossing on Mountain Air Drive is a single span 148' long precast

concrete decked-bulb tee bridge over alignment 1. The bridge will have approaches that are

approximately 50’ long on each end of the bridge.

Appendix K provides a bridge analysis for the three alternative alignments.

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21.0 EXCEPTIONS TO DESIGN STANDARDS

There are no exceptions to design standards for this project.

22.0 MAINTENANCE CONSIDERATIONS

Future maintenance will be the responsibility of the Municipality of Anchorage.

23.0 ITS FEATURES

All NHS and non-NHS highway projects receiving federal funding and incorporating Intelligent

Transportation System (ITS) elements are required to be developed in conformance with 23 CFR 940

National Intelligent Transportation System Architecture and Standards.

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AMATS: Mountain Air Drive Extension Design Study Report

APPENDIX A

Approved Design Criteria and Design Designation

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PROJECT DESIGN CRITERIA Page 1 of 3

Project Name: AMATS: Mountain Air Drive Extension

State Project No.:

UAA CED 2021.02 Federal Project No.: N/A

Functional Classification:

Rural Neighborhood Collector Terrain: Rolling

Segment: Rabbit Creek Rd. to Sandpiper Dr

Present ADT (2021): N/A Mid-Design ADT (2038): N/A Design ADT (2048): 3416

DHV (%): N/A Trucks (%): N/A Directional Split (%/%): N/A

Pavement Design Year: 20 Pavement Design ESAL: N/A

Design Turning Vehicle: WB-67

Project Type: New Construction/Reconstruction NHS: ☐ Non-NHS: ☐

FHWA 10 CONTROLLING DESIGN CRITERIA

SOURCE

STA

ND

AR

D

AS

PR

OP

OSE

D

EXC

EPTI

ON

1

Design Speed1 MOA DCM Table 1-4, Pg. 1-25 35 mph 35mph No

Lane Width Travel MOA DCM Table 1-4, Pg. 1-25 10-11 ft 11 ft No

Auxiliary MOA DCM Table 1-4, Pg. 1-25 10-11 ft 11 ft No

Shoulder Width

Outside MOA DCM Table 1-4, Pg. 1-25 3.5-5 ft 5 ft No

Inside N/A N/A ft N/A N/A

Auxiliary N/A N/A ft N/A N/A

Horizontal Curve Radius, min MOA DCM Table 1-9, Pg. 1-51 600 ft > 600 ft No

Superelevation Rate, e, max MOA DCM Table 1-10, Pg. 1-

55 6% ≤ 6% No

Stopping Sight Distance (SSD), min

MOA DCM Fig. 1-20, Pg. 1-54 250 ft > 250 ft No

Grade Min. MOA DCM Pg. 1-45 1% 1% No

Max. MOA DCM Table 1-8 Pg. 1-47 ≤ 8% 5% No

Cross Slope MOA DCM Pg. 1-47 2-3% 2% No

Vertical Clearance, Overhead Utilities

HPCM Table 1130-1, Pg. 1130-5

20 ft – 6 in 20 ft – 6 in No

Design Loading Structural Capacity1 GB Pg 6-7, Sec. 6.2.3 HL 93 HL 93 No

1 On low speed roadways (<50 mph) on the NHS, only Design Speed and Design Loading Structural Capacity require a Design Exception; all other criteria require a Design Waiver. For projects off the NHS, all criteria require a Design Waiver.

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Page 2 of 3

OTHER DESIGN CRITERIA

SOURCE

STA

ND

AR

D

AS

DES

IGN

ED

WA

IVER

Superelevation Transition, Δ GB Table 3-15 Pg. 3-61 0.62% 0.62% No

Bridge Clear-Roadway Width HPCM Pg. 1160-15, Sec.

1160.3.5 N/A N/A N/A

Vertical Curvature (min)

K (crest) GB Table 3-34 Pg. 3-155 29.0 29 No

K (sag) GB Table 3-36 Pg. 3-161 49.0 49 No

Lateral Offset to Obstruction RDG Pg. 10-1 4-6 ft 4 ft No

Surfacing Material HPCM Pg. 1180-1, Sec.

1180.3 Paved Paved No

Clear Zone

Slope (fill)

HPCM Pg. 1130-6, Table

1130-2

4:1 or flatter

4:1 or flatter

No

Width (fill) 14-16 ft 19 ft No

Slope (cut) N/A N/A N/A

Width (cut) N/A N/A N/A

Bicycle Lane Width N/A N/A N/A N/A

Sidewalk/Pathway Width MOA DCM Table 1-4, Pg. 1-

25 5 ft/8 ft 5/8 ft No

Intersection Sight Distance, Passenger Car

Left Turn (GB Case B1)

GB Table 9-6 Pg. 9-38 385.9 ft 390 ft No

Right Turn (GB Case B2)


Crossing (GB Case B3)


Passing Sight Distance GB Table 3-4 Pg. 3-9 550 ft 550 ft No

Degree of Access Control GB 2.5.4 Pg. 2-73 Driveway regulations No

Median

Treatment

N/A

N/A N/A

Width N/A N/A N/A

Illumination DCM 5.4H Pg. 5-9 Intersection illumination No

Curb Type N/A N/A N/A

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Page 3 of 3

Notes: GB = Green Book, DCM = Design Criteria Manual, HPCM= Highway Preconstruction Manual, RDG = AASHTO Roadside Design Guide Proposed by: Date: Designer (Consultant or Staff) Recommended by: Date: Engineering Manager Accepted by: Date: Regional Preconstruction Engineer

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APPENDIX B

Typical Sections

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APPENDIX C

3R Analysis

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APPENDIX D

Traffic Analysis

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The information in this report is compiled for highway safety planning purposes. Federal law prohibits its

discovery or admissibility in litigation against state, tribal or local government that involves a location or

locations mentioned in the collision data. 23 U.S.C. § 409; 23 U.S.C. § 148(g); Walden v. DOT, 27 P.3d

297, 304-305 (Alaska 2001).

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APPENDIX E

Material Recommendations

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APPENDIX F

VE Consideration

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APPENDIX G

Approved Environmental Document

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APPENDIX H

Approved Design Exceptions and Design Waivers

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APPENDIX I

ITS Systems Engineering Analysis

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APPENDIX J

Design Memos

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APPENDIX K

Bridge Analysis

An alternatives analysis was developed for all three alternative alignments. Possible structures to cross

Little Rabbit Creek include a single-span 148' or two-span 260' precast concrete decked bulb-tee bridges,

multi-plate culverts, and concrete culverts. Each alternative alignment crossing structure was tailored to

accommodate the respective alignment location elevations and 100-year flood plain levels for Little

Rabbit Creek.

ALIGNMENT 1 – PREFERRED ALTERNATIVE

Alignment 1 crossing alternatives included both the single-span 150' precast concrete decked bulb tee

bridge and the two-span 260' precast concrete decked bulb tee bridge. Bridges were considered at this

location because of the steep slopes above the creek. A bridge would allow the road to have a less steep

grade on the approach by raising the deck elevation in comparison to a culvert. The bridges that were

considered are 260’ and 148’ long. The girders on the single-span bridge would be 145’ long and two

130’ long on the two-span bridge. The 148' bridge has longer and more expensive girders but requires less

fill material and eliminates the need for a pier. The 260' bridge requires shorter girders and are less

expensive but require a larger amount of fill material and a pier to be placed in the middle of Little Rabbit

Creek. Another option is a steel bridge, but it would be more expensive than the single or two-span

precast concrete bridge. The single span 148' long precast concrete deck bulbed-tee bridge is the preferred

alternative. The quantities and cost of materials for the single span 148’ long bridge is in the table below.

Item No. Item Est Unit

Total Quantity

Cost/ Unit Cost

205.0006.0000 Structural Fill CY 1,300 35 $45,500

501.0001.000 Class A Concrete CY 180 1,500 $270,000

501.0007.0000 Precast Concrete Member, 145'-0" Decked Bulb-Tee EA 9 65,000 $585,000

503.0001.0000 Reinforcing Steel LBS 12,000 1.75 $21,000

503.0002.0000 Epoxy-Coasted Reinforcing Steel LBS 24,000 2 $48,000

503.2000.0000 Waterproofing Membrane, Spray Applied SY 910 100 $91,000

505.0005.1417 Furnish Structural Steel Piles, HP 14x117 LF 900 80 $72,000

505.2005.1417 Install Structural Steel Piles, HP14x117 EA 14 10,000 $140,000

504.0001.0002 Steel Bridge Railing, 3-Tube LF 380 200 $76,000

507.0001.0002 Steel Bridge Railing, Pedestrian Rail LF 380 200 $76,000

511.0001.0000 Mechanically Stabilizing Earth Wall SF 1,840 65 $119,600

606.0016.0000 Transition Rail EA 4 2,500 $10,000

611.0001.0002 Riprap, Class II CY 800 75 $60,000

TOTAL $1,614,100

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This alignment has steep slopes with a ravine approximately 40' deep. The 100-year flood has a flood

plain that is about 38' wide and about 4' high. The bridge is supported by an approximately 20' tall MSE

walls at the abutments with a 2.5:1 slope on each side of the approach. The area under the bridge is large

enough that flooding that would impact the bridge and debris buildup are unlikely to ever be a concern

and there is plenty of space for wildlife crossing. The height of the MSE walls were decided to balance

increasing costs and engineering after a 20' tall cut was required to bring the road down to bridge deck

elevation. The approaches are longer and the bridge deck elevation lower to balance the cost between the

roadway and structural components. This bridge will have H-piles that are installed 50’ below ground

level at the abutments creating a deep foundation.

The longitudinal slope of the bridge is 0.7% to allow proper drainage of the bridge deck. The pavement,

both the roadway, pathway, and sidewalk and paved and have a 2% cross slope to allow for drainage.

A 3-tube pedestrian railing is between the roadway and the pathways which has a height of 3’-8” and

pedestrian rail is on the outside of each pathway, which is 4’-6” tall. The roadway has 4’ shoulders and

11' wide lanes. The sidewalk is 5’-6” wide and the pathway is 8’-0” wide. The new standard thrie-beam

transition rail will be installed in each corner of the bridge and will provide adequate distance and

protection for pedestrians as their pathways near the roadway during the roadway-bridge transition.

ALIGNMENT 2

Alignment 2 crossing alternatives included the 148’ single-span precast concrete decked bulb tee bridge

and a low-profile multi-plate culvert. The 148’ bridge considerations are the same as those indicated for

Alignment 1. The multi-plate culvert would be 18’-8” tall and 45' wide to accommodate the 100-year

flood plain level.

The culvert would be manufactured out-of-state and shipped up and would require a large amount of fill

material. However, the existing ground slopes on either side the creek at Alignment 2 are less steep than

Alignment 1 requiring shorter fill and side slopes. Although the multiplate culvert would be considerably

large, require a great deal of fill material, and be manufactured out-of-state, the cost analysis of the

multiplate culvert versus the single-span 148’ precast concrete decked bulb tee bridge determined the

multiplate culvert to be less expensive. Additionally, because the culvert would be very wide, it poses less

of a concern for debris or ice buildup than that of smaller culverts during a flood event. Though not a

requirement for this area, this culvert is also tall enough to be considered a wildlife passage.

ALIGNMENT 3

Alignment 3 crosses two branches of Little Rabbit Creek which requires two crossings. Alignment 3

considers two types of culverts: a concrete box culvert and a steel multiplate culvert. The stream crossings

are a shorter horizontal and vertical distance, and the streams are smaller than in comparison to

Alignments 1 and 2. The recommended structure are two multi-plate culverts are 20’ long and 10’ tall.

Due to the shorter spans, a bridge is not recommended for this alignment.

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During construction, the streams would need to be diverted since a sheet pipe foundation would be

installed. A sheet pile foundation was preferred over a spread footing foundation because of ease of

construction and resilience in seismic events. The multiplate structures would need to be shipped up while

precast culverts could be constructed locally. In the case of a flood event, the water would rise above the

foundation and while it is unlikely to overflow the culvert, debris and ice could create problems in the

future. A concrete box culvert would have similar advantages and disadvantages.

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APPENDIX L

Alternative Analysis Memo

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MOUNTAIN AIR DRIVE ALIGNMENT ALTERNATIVES

A weighted-average matrix was used to select the preferred alternative alignment consisted of the

following criteria: capital costs, future maintenance costs, environmental impact, mobility and

accessibility, and public opinion. With the direct and indirect budgets involved with the project, capital

costs were the most heavily weighted, and future maintenance costs were also considered. Other criteria

were weighted according to their relation with primary and secondary purpose and needs for the project,

and their anticipated value for the public and client.

Table 1 displays the criteria matrix and rankings for the Alternative Alignments.

The No Build alternative was considered and was assigned values for each criterion.

For capital costs, the higher the value, the cheaper the alternative. When comparing between the

alternatives, assigned values were primarily balanced between total linear feet of roadway, the type of

structural crossing, potential right-of-way (ROW) acquisitions, and potential utility conflicts.

When analyzing the considerations, for total feet of roadway, Alignment 1 has the shortest potential

roadway through the project area, with Alignment 2 being only a few hundred feet longer. Alignment 3 is

much longer than the other two. For the crossing, Alignment 1 is designed with a single-span bridge,

Alignment 2 has a multi-plate arch culvert, and Alignment 3 has two multi-plate arch culverts. For ROW,

Alignments 1 and 2 project to acquire a significant amount of ROW. Alignment 3 primarily follows

Municipality of Anchorage (MOA) platted ROW around the project area, although will need additional

ROW. For potential utility conflicts, Alignment 1 and 2 have similar utility impacts. For several hundred

feet of Alignment 3, hanging utilities are next to the designed corridor. Further investigation is needed to

determine if the hanging utilities will need to be relocated.

For future maintenance costs, the higher the value, the cheaper the alternative. When comparing the

alternatives, assigned values were primarily between total linear feet of roadway to be maintained, and the

type of structural crossing.

When analyzing the considerations, for total feet of roadway to be maintained, especially in the winter,

Alignment 1 has the shortest potential roadway through the project area, with Alignment 2 being only a

few hundred feet longer. Alignment 3 is much longer than the other two. For the structural crossings, the

single-span bridge for Alignment 1 would require biennial inspections. The culverts designed for

Alignment 2 and 3 do not require inspections.

For environmental impact, the higher the value, the greater the impact. When comparing between

alternatives, assigned values were primarily balanced between proximity to MOA-classified wetlands,

presence with respect to the floodplain of Little Rabbit Creek, and potential impacts with wildlife.

When analyzing the considerations, for proximity to wetlands, Alignment 1 avoids all area defined

wetlands. Alignment 2 does not encroach, but comes near some wetlands that are to the east of the

alternative. Alignment 3 crosses through wetlands on the east side of the project area and passes next to

other wetlands before reaching the cul-de-sac. For the impact on Little Rabbit Creek, the retaining wall

for the single-span bridge does not enter the 100-year floodplain. The culverts for Alignments 2 and 3 will

be installed in the 100-year floodplain. For wildlife impacts, the single-span bridge for Alignment 1

would not impact the game trails along Little Rabbit Creek. The culverts for Alignments 2 and 3 need

further analysis to consider potential interactions with area wildlife, including bull moose and

anadromous fish.

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For mobility and accessibility, the higher the value, the stronger the perception that alternative meets the

characteristic. Other collector roads in the area, Goldenview Drive to the west, and Clarks Road to the

northeast, were used as comparables for the new Mountain Air Drive alignment.

When analyzing the characteristics over the undeveloped project area, for mobility, Alignment 1 does not

have any stop-controlled intersections, and all curve radii are larger than the DCM recommended

minimum of 600 feet (Table 1-9). It was designed to perform similarly to the comparables and directly

address the purpose and need of the project, secondary egress and secondary access for emergency

services, and serves as a mainline thoroughfare through the project area. Alignment 2 has one stop-

controlled intersection. Alignment 3 has three stop-controlled intersections. Alignment 2 and 3 are

constrained by the corner at the southwest corner of Bear Valley Elementary School (BVES). To avoid

acquiring school property, the alignments were designed with a curve radius less that the DCM

recommended minimum. For accessibility throughout the vicinity, Alignment 1 does not project to

provide direct access to future residents, and local roads would need to be installed to develop the area.

Alignment 2 projects to serve slightly more parcels than Alignment 1. Following MOA platted ROW

around the project area, Alignment 3 addresses a secondary purpose and need of the project for future

development with its route.

For public opinion, alternatives were assigned values from public feedback. At the time of ranking, public

opinion data showed an interest in moving forward with the project, but no data existed in differentiating

the alternative alignments.

Table 1: Alignment Criteria Matrix Rankings

RABBIT CREEK ROAD / MOUNTAIN AIR DRIVE INTERSECTION ALTERNATIVES

The intersection matrix used the following criteria to determine the selection of the preferred alternative:

the cost, maintenance, public opinion, traffic flow, safety, and flexibility.

Table 2 displays the criteria matrix and rankings for the Alternative Alignments.

The cost is regarding the initial cost of the alternative and the maintenance is regarding the cost over time

to maintain that alternative. The higher the value, the cheaper the alternative is. The no-build option has

the highest rating for these two criteria, as it will have need minimal cost to maintain the current

condition. The traffic signal is the lowest rated amongst the other alternatives, as the initial cost of the

traffic signal is the highest amongst the others. Traffic signals would require the multi-conductor cables to

be installed and signal wiring to be implemented underneath the roads. The maintenance cost of the traffic

signal is also approximately $10,000.00 per year. The roundabout and turn lanes alternative were rated in

the middle, as it is not as expensive as traffic signals, but still requires a significant cost. Turn lanes would

require an additional ROW acquisition and reallocation of the cross-section to include additional turn

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lanes on the road. In order to account for a traffic signal to be installed in the future when traffic volumes

increase, signal wiring should be installed in preparation. The roundabout has a higher upfront cost due to

the installation of the roundabout design but would not require any special maintenance cost like a traffic

signal would.

The public opinion was based on the Rabbit Creek Community Council meeting. The public was in favor

of improvements being done and preferred a roundabout to be placed at the intersection between Rabbit

Creek Road and Mountain Air Drive. Thus, the roundabout was rated higher than the other alternatives

due to the community’s opinion.

The traffic flow is in regard to how stable the flow of traffic is due to these improvements. In its current

condition, should the Mountain Air Drive extension be built, the level of service would go from a rating

of B (Stable Flow, slight delays) to F (Forced flow, jammed) based on the USKH study. An acceptable

level of service is a minimum of rating D (Approaching unstable flow). The roundabout was rated highest

in the design criteria matrix, as the level of service would exceed the others. The turn lane would have an

acceptable flow of traffic, but would require a traffic signal to be installed when traffic volumes increase.

The improper usage of a traffic signal would cause delays at the intersection, so it must be used in

conjunction with a turn lane.

The safety criteria is in regards to the safety of both the drivers and pedestrians. Studies have shown that

roundabouts are the safest in terms of preventing crashes. Turn lanes were the next highly rated

alternative, as providing an additional lane specifically for through-traffic prevents the severity of crashes

at the intersection. Traffic signal, while provides an easier understanding for pedestrian crossing, does not

prevent the severity of crashes as much as the other alternatives do.

The flexibility criteria was based on its usefulness in the future should further expansion be done in the

area. Turn lanes allow the intersection to also install a traffic signal should traffic volumes increase. A

single-lane roundabout can later be upgraded to a multilane roundabout to accommodate for an increase

in traffic volume. A traffic signal installed in its existing condition would require the installation of turn

lanes, as it would be a detriment to the traffic flow and can cause further delays during the peak AM and

PM hours.

Table 2: Intersection Criteria Matrix Rankings

amats: mountain a rive extension

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