Seward Highway, MP 75-90 Rehabilitation Project - Portage Curve

Project No.: OA3/58105

DESIGN STUDY REPORT

STATE OF ALASKA DEPARTMENT OF TRANSPORTATION AND PUBLIC FACILITIES

PREPARED BY:

Seawolf Engineering, Inc. 2900 Spirit Drive, Room 205 Anchorage, AK 99507

Revised June 2016

STATE OF ALASKA

DEPARTMENT OF TRANSPORTATION AND PUBLIC FACILITIES DESIGN AND ENGINEERING SERVICES – CENTRAL REGION

DESIGN STUDY REPORT

For

Seward Highway, MP 75-90 Rehabilitation Project – Portage Curve

Project No.: OA3/58105

Written by: Zach Cuddihy, Kelsey Copley, Kyle Powell, Grant Warnke

Prepared by:

______Zach Cuddihy Date Student Project Manager

Concur by:

______Randy D. Vanderwood, P.E. Date Project Manager

Concur by:

______James E. Amundsen, P.E. Date Chief, Highway Design

Approved:

______Wolfgang E. Junge, P.E. Date Preconstruction Engineer

NOTICE TO USERS

This report 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, Randy Vanderwood, P.E. at (907) 269-0586 for this information.

PLANNING CONSISTENCY

This document has been prepared by the Department of Transportation and Public Facilities according to currently acceptable design standards and Federal regulations, and with the input offered by the local government and public. The Department's Planning Section has reviewed and approved this report as being consistent with present community planning.

CERTIFICATION

We hereby certify that this document was prepared in accordance with Section 520.4.1 of the current edition of the Department's Highway Preconstruction Manual and CFR Title 23, Highway Section 771.111(h).

The Department has considered the project's social and economic effects upon the community, its impacts on the environment and its consistency with planning goals and objectives as approved by the local community. All records are on file with Central Region - Design and Engineering Services Division, Highway Design Section, 4111 Aviation Avenue, Anchorage, AK 99502.

Wolfgang E. Junge, P.E. Date Todd Vanhove Date Preconstruction Engineer Chief, Planning

TABLE OF CONTENTS LIST OF FIGURES ...... ii LIST OF APPENDICES ...... ii LIST OF ACRONYMS ...... ii 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 ...... 1 2.0 DESIGN STANDARDS AND GUIDELINES ...... 2 3.0 DISCUSSION OF ALTERNATIVES ...... 2 3.1 First Alternative – No-Build ...... 3 3.2 Second Alternative – Re-alignment Only ...... 3 3.3 Third Alternative – Re-alignment and Turning Lanes ...... 3 4.0 PREFERRED ALTERNATIVE ...... 3 5.0 TYPICAL SECTIONS ...... 4 6.0 HORIZONTAL AND VERTICAL ALIGNMENT ...... 4 6.1 Horizontal Alignment ...... 4 6.2 Vertical Alignment ...... 4 7.0 EROSION AND SEDIMENT CONTROL ...... 4 8.0 DRAINAGE ...... 5 8.1 MS4 Permit ...... 5 9.0 SOIL CONDITIONS ...... 6 10.0 ACCESS CONTROL FEATURES ...... 6 11.0 TRAFFIC ANALYSIS ...... 6 12.0 SAFETY IMPROVEMENTS ...... 6 13.0 RIGHT-OF-WAY REQUIREMENTS ...... 6 14.0 PEDESTRIAN AND BICYCLE FACILITIES ...... 7 15.0 UTILITY RELOCATION AND COORDINATION ...... 7 15.1 GCI ...... 7 15.2 Chugach Electric ...... 7 16.0 PRELIMINARY WORK ZONE TRAFFIC CONTROL ...... 7 16.1 Traffic Control Plan (TCP) ...... 8 16.2 Public Information Plan (PIP) ...... 8 16.3 Transportation Operations Plan (TOP) ...... 8 17.0 STRUCTURAL SECTION AND PAVEMENT DESIGN ...... 8 18.0 COST ESTIMATE ...... 9 19.0 ENVIRONMENTAL COMMITMENTS AND CONSIDERATIONS ...... 9 20.0 BRIDGES ...... 10 21.0 EXCEPTIONS TO DESIGN STANDARDS ...... 10 22.0 MAINTENANCE CONSIDERATIONS ...... 10 23.0 ITS FEATURES ...... 10

Seward Hwy MP 75-90 – Portage Curve i Design Study Report

LIST OF FIGURES

Figure 1 Location & Vicinity Map

LIST OF APPENDICES

Appendix Description A Approved Design Criteria and Design Designation B Typical Sections C Material and Geotechnical Recommendations D Traffic Analyses (signal warrants, capacity analysis, roundabout analysis, etc.) and speed studies E Hydraulic and Hydrologic Report F Bridge Preliminary Design

LIST OF ACRONYMS

AADT Annual Average Daily Traffic AASHTO American Association of State Highway and Transportation Officials ACGP Alaska Construction General Permit ADEC Alaska Department of Environmental Conservation APDES Alaska Pollutant Discharge Elimination System ARRC Alaska Railroad Corporation ATM Alaska Traffic Manual BMP Best Management Practice CFR Code of Federal Regulations DOT&PF Alaska Department of Transportation and Public Facilities ESCP Erosion and Sediment Control Plan EPA Environmental Protection Agency FHWA Federal Highway Administration HPCM Alaska Highway Preconstruction Manual HMCP Hazardous Material Control Plan HSIP Highway Safety Improvement Program LOS Level of Service MADT Monthly Average Daily Traffic MOA Municipality of Anchorage MP Milepost MPH Miles Per Hour MUTCD Manual on Uniform Traffic Control Devices NPDES National Pollutant Discharge Elimination System PGDHS A Policy on Geometric Design of Highways and Streets PIP Public Information Plan ROW Right-of-Way SWMM Storm Water Management Model SWPPP Storm Water Pollution Prevention Plan TCP Traffic Control Plan TMP Traffic Management Plan USGS United States Geological Survey

Seward Hwy MP 75-90 – Portage Curve ii Design Study Report

Figure 1 Location and Vicinity Map

Seward Highway MP 75-90 – Portage Curve 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) proposes to reconstruct the portion of the Seward Highway between Milepost (MP) 78 and 79. The project is located in Section 5 Township 8N and 9N, Range 3 E., Seward Meridian, USGS Topographical Map Anchorage D-6; Latitude 60.819629° North, Longitude 148.975578° West, within the Municipality of Anchorage (MOA), near the community of Girdwood, Alaska. See Figure 1 for Location and Vicinity Map.

The proposed reconstruction consists of: building a new section of road between MP 78 and 79 and constructing new bridges over Placer River and Portage Creek #1. Work also includes removing existing bridges, adding new striping, and relocating and constructing utilities.

1.2 Existing Facilities and Land Use

The Seward Highway is the sole connection by land for the Kenai Peninsula and Whittier to Anchorage. The roadway between MP 78 and 79 spans two rivers, Placer and Portage Creek No. 1. Each bridge has been retrofitted to increase its seismic capacity, but by current standards the bridges are still not at an adequate capacity for seismic loading. The last major earthquake was the Good Friday Earthquake of 1964 which caused irreparable damage to the bridges that the current ones replaced. An earthquake of that magnitude has the potential to cause similar damage to the existing bridges, which means the Kenai Peninsula and Whittier could be cut off from the road system.

The existing roadway consists of 12-foot lanes and 8-foot shoulders. Additionally, the traffic volumes on the roadway vary drastically depending on the season. Summer months can see more than 10,000 vehicles per day on peak weekends, whereas winter months generally see less than 2,000 vehicles per day. The estimated average daily traffic (ADT) in the design year is approximately 6,000 vehicles per day.

The land surrounding the right-of-way is owned by Chugach National Forest, the Alaska Railroad Corporation, and privately corporations. Additionally, historic cultural sites are located near the Portage-Glacier Road intersection. These sites are remnants of houses and structures that were destroyed in the 1964 earthquake.

1.3 Purpose and Need

The purpose of this project is to improve safety for the traveling public, provide an acceptable Level of Service (LOS) for anticipated traffic with the 20-year design life, and address the structurally deficient bridges at Portage Creek #1 and Placer River. This section of road has a broken-back curve that limits the sight distance, doesn’t meet current AASTHO standards for minimum radius of curvature for the existing speed limit, and creates a higher potential for vehicular crashes. In addition, both bridges located within this project have a bridge deck rating below 4, and the bridges do not meet current structural code requirements for seismic and live-loading capacity.

Between 1999 and 2008, a total of 27 reported vehicle incidents were logged within the one-mile project limit. Crashes in the summer and winter months were mainly due to rear-end collisions and loss of control due to poor road conditions, respectively. In the summer, six out of the nine reported crashes were caused by vehicles that were stopped or turning. The lack of turning lanes, and a reduced stopping

Seward Highway MP 75-90 – Portage Curve 1 Design Study Report

sight distance due to the broken-back curve, increased the potential for crashes of this nature. During winter months, 13 of the 18 crashes were the result of slick road conditions due to ice or snow. The sharp broken-back curve contains a sharp transition between two tangents which decreases the drivers’ ability to maintain their vehicle at a high speed, especially on road conditions that are less than adequate.

The proposed design would add dedicated turn lanes to major intersections, realign the horizontal curve to meet current AASHTO standards for minimum radius of curvature, and add newly designed bridges that meet current LRFD capacities.

2.0 DESIGN STANDARDS AND GUIDELINES

Design standards and guidelines that apply to the Seward Highway MP 75-90 – Portage Curve Project are contained in the following publications:

Standards:

 ADA Standards for Accessible Design, United States Department of Justice, September15, 2010 except for the use of Detectable Warnings on Curb Ramps standards as stated in the ADA Standards for Transportation Facilities, United States Department of Transportation (U.S. DOT), 2006.  A Policy on Geometric Design of Highways and Streets (PGDHS or “Green Book”), American Association of State Highway and Transportation Officials (AASHTO), 2001.  Alaska Highway Preconstruction Manual (HPCM), State of Alaska, Department of Transportation and Public Facilities, 2005 (including all revisions thru August 2014).  The Alaska Traffic Manual (ATM), consisting of the Manual on Uniform Traffic Control Devices (MUTCD), 2009 as amended, U.S. Department of Transportation, Federal Highway Administration (FHWA) and the Alaska Traffic Manual Supplement, State of Alaska, Department of Transportation and Public Facilities, 2016.  Guide for the Development of Bicycle Facilities, AASHTO, 1999.  Guide for the Planning, Design, and Operation of Pedestrian Facilities, AASHTO, 2004.  An Informational Guide for Roadway Lighting (IGRL), AASHTO, 1984.  Roadside Design Guide, 3rd Edition, AASHTO, 2002.

 Intersection Channelization Design Guide, Transportation Research Board, 1985.

Appendix A contains the project Design Criteria and Design Designation.

3.0 DISCUSSION OF ALTERNATIVES

Multiple improvement options were analyzed for the Preliminary Engineering Report (PER) of the Seward Highway between MP 78 and 79. The alternatives are discussed below:

Seward Highway MP 75-90 – Portage Curve 2 Design Study Report

3.1 First Alternative – No-Build

The first alternative is the No-Build alternative. Under this alternative the Seward Highway will continue to follow the broken-back curve. The existing curve contains an approximate radius of 1300 feet, which is inadequate for motorized travel at the current design speed of 60mph. Additionally, the intersections at the Alaska Wildlife Conservation Center and Portage-Glacier Road would remain unchanged; continued rear-end collisions will continue because of this. Lastly, both structurally deficient bridges would remain in-place, unchanged from their current condition. The bridge deck condition will continue to deteriorate with more repeated cycles of traffic passing over them. Based on the above considerations, this alternative was rejected.

3.2 Second Alternative – Re-alignment Only

The second alternative would realign the Seward Highway between MP 78 and 79; impacts to wetlands would be the result of the realignment. Seward Highway would remain at two-lanes without the addition of turning lanes at the Alaska Wildlife Conservation Center and Portage-Glacier Road. Furthermore, with the change to the alignment of the road, new bridges will need to be constructed. Based on the above considerations, this alternative was rejected because it doesn’t solve an important consideration: intersection safety.

3.3 Third Alternative – Re-alignment and Turning Lanes

The third alternative would realign the Seward Highway between MP 78 and 79 and add turning lanes to both intersections. Seward Highway would have an additional northbound lane added between the Portage-Glacier Road and Alaska Wildlife Conservation Center intersections. The byproduct of this alternative would be a larger impact to the surrounding wetlands. This alternative also includes the construction of new bridges, which means that all requirements of the project have been met. Based on the above considerations, this alternative was selected for the project.

4.0 PREFERRED ALTERNATIVE

The preferred alternative was the third alternative because it improves the existing road and solves the issue of safety in this corridor. The addition of turning lanes at both intersections will allow vehicles to safely move out of the flow of traffic which effectively reduces the risk of a rear-end collision. An extended merging lane will be added for vehicles turning northbound onto the Seward Highway from Portage-Glacier Road. This is aimed at allowing large vehicles, namely the design vehicle: WB-109D, to successfully enter the flow of traffic once they’ve reached the posted speed limit. Additionally, the curve will be designed to meet current AASHTO standards for a 60 mph design speed. This will improve the safety of vehicles moving through this corridor, especially during winter months when road conditions are less than optimal.

The existing, structurally deficient bridges would be removed and new bridges would be built along the new alignment. Both bridges would be designed and built meeting current AASHTO LRFD capacities and standards. This option is preferred over rehabilitating the existing bridges because much of the structural system will be unable to be improved in the manner that is required.

This alternative results in a significant impact to the surrounding wetlands. An environmental review and permitting process will need to be conducted with the US Army Core of Engineers.

Seward Highway MP 75-90 – Portage Curve 3 Design Study Report

5.0 TYPICAL SECTIONS

The mainline typical section remains as two 12-foot lanes, one in each direction, with eight-foot shoulders. The typical also includes a foreslope of 4:1 and a backslope of 6:1. The roadway is widened near the Portage-Glacier Road intersection to accommodate a dedicated southbound left turn lane and a dedicated right-hand turn lane for northbound traffic. No depressed medians were added to the intersection, instead, striping will be added.

Rumble strips will be installed on the shoulders of the new mainline.

The typical sections are provided in Appendix B.

6.0 HORIZONTAL AND VERTICAL ALIGNMENT

6.1 Horizontal Alignment

6.1.1 Seward Highway

A simple curve was chosen for the main alignment of the Seward highway to maintain a constant maximum super elevation for the Portage Creek and Placer River bridges. Based on a design speed of 60mph, and max super elevation of 6%, the final radius was chosen at 2150 feet. The resulting super elevation of the curve was calculated at 3.8%, which is also maintained on the Portage Creek and Placer River bridges. The Portage-Glacier Road intersection at the Seward highway is based on a WB-20 semitrailer with compound curves of 440 feet, 65 feet and 440 feet.

6.1.2 Portage Highway

A simple curve was also used for the Portage Glacier highway leading up to the Seward highway intersection. The speed limit before the intersection and curve was reduced to 35 mph to improve safety around the curve and the resulting intersection. Because of a reduced speed, a minimum curvature of 730 feet is required. Thus, the maximum super elevation for this curve is 3.4%.

6.1.3 Wildlife Center:

The new Wildlife Center realignment will be posted at 15mph and contain a curve of 180 feet. A Single unit bus was used for the calculation of the turn lanes at the intersection of the Wildlife Center road and the main Seward Highway alignment. Thus, a simple curve was used for the intersection, which contain radii of 50 feet.

6.2 Vertical Alignment

Per AASHTO, the minimum sag and crest K values for a highway at 60mph will 136 and 1628, respectively. Grades are maintained at 0% along the bridges. The percent grade remains less than 1% throughout the alignment since the elevation is relatively constant along the project length.

7.0 EROSION AND SEDIMENT CONTROL

The project includes temporary and permanent measures to control or prevent erosion and sedimentation during and post project construction. The contractor will prepare a Storm Water Pollution Prevention Plan

Seward Highway MP 75-90 – Portage Curve 4 Design Study Report

(SWPPP) prior to construction that conforms to the DOT&PF Best Management Practices (BMPs) for Erosion and Sediment Control in accordance with the DOT&PF contract specifications and follows the guidelines of the Erosion and Sediment Control Plan (ESCP) provided to the contractor. The contractor will submit the SWPPP for approval by the Construction Project Engineer. The contractor will conduct construction activities in accordance with the approved SWPPP. Temporary BMP’s will remain in place until permanent erosion and sediment control measures are in place and soil is permanently stabilized.

8.0 DRAINAGE

The proposed typical sections and corridor will not have any depressed medians or ditches. However, the proposed corridor will have a 3.8% super-elevation around the proposed curve. Additionally, the entire corridor is on wetlands. Therefore, this local review of the project contains a preliminary drainage study based on the surrounding area and a 100-year storm event. The 100-year storm even must be used since FEMA classifies the project area as a special flood hazard area (SFHA) subject to inundation by the 1% annual chance flood. Additionally, per the Alaska Highway Drainage Manual, Chapter 7 – Appendix A, culverts in designated flood hazard areas require the 100-year storm event.

The preliminary drainage design only considers the drainage basins to the West of the road that will drain East towards the road. See the figure below for more details of the basins. As stated before, these basins are all wetlands, which will cause some storage and stage effects that were not considered in the current 35% design. The area is also almost flat, but was found to slope towards the East. The shallow slope may cause more storage and infiltration effects that were also not considered. However, the resulting storm flow rate will be a valid representation for the area at a local review level.

The culvert sizes were chosen based on this preliminary drainage study as well as being in accordance with the Alaska Highway Drainage Manual. See Appendix E for the entire Hydraulic and Hydrologic Report.

8.1 MS4 Permit

The National Pollutant Discharge Elimination System (NPDES) Program originated under section 402 of the Clean Water Act (CWA, 33 USC §1251), requires that pollutant discharges to surface water be authorized by permit. Together, the Municipality of Anchorage (MOA) and the DOT&PF are authorized to do so through an Authorization to Discharge permit under the National Pollutant Discharge Elimination System. This authorization, Alaska Pollutant Discharge Elimination System (APDES) Permit No. AKS 052558, is effective from August 1, 2015 to July 31, 2020. This permit applies to projects within the MOA.

To comply with the intent of the permit; the project will use, at a minimum, control measures to comply with BMPs and the Storm Water Management Program (SWMP), and follow the Authorization to Discharge under the APDES.

• The project follows the criteria set forth in the DOT&PF’s Alaska Highway Drainage Manual and the MOA’s Drainage Design Guidelines. • The contractor will develop a SWPPP prior to construction that follows the guidelines of the ESCP provided to the contractor. The SWPPP will comply with the APDES permitting program and the Alaska Construction General Permit (ACGP). • The contractor will describe how to minimize and manage to reduce pollution to storm water in the contractor’s SWPPP. • The contractor will comply with all permit conditions with respect to installation and maintenance of control measures, inspections, monitoring (if necessary), corrective actions, reporting and recordkeeping.

Seward Highway MP 75-90 – Portage Curve 5 Design Study Report

• The contractor will address all discharge in the SWPPP. The contractor will prepare a Hazardous Material Control Plan (HMCP). • The maintenance of the pipes, sewers, and other conveyances will remain the responsibility of the State of Alaska. • State of Alaska will maintain outreach and education through the State of Alaska website. Project specific information will be posted at the project site once construction activity begins.

9.0 SOIL CONDITIONS

A geotechnical report is being developed for this project. A field investigation completed by Shannon & Wilson, Inc., indicated this project contains a large degree of silt deposits with a ground water table consistently at surface level. The silt deposits near the surface are classified as “loose to very loose” due to the blow counts from the test holes being less than 5. A large amount of fill will be placed on top of conditions such as these, and a varying degree of settlement is expected.

Material and geotechnical recommendations can be found in Appendix C.

10.0 ACCESS CONTROL FEATURES

New access to the highway will be managed through driveway permits and future project evaluation. A new access point to the Alaska Wildlife Conservation Center is included with the design to allow continued access to the facility during construction.

11.0 TRAFFIC ANALYSIS

A traffic analysis is being prepared for this project. With the addition of turning lanes at both intersections within the project, turning movements were analyzed to determine the percentage of vehicles that were turning. Utilizing projected ADT values and the percentage of turning vehicles, storage lengths for the required intersections were computed. The addition of these turn lanes is in response to the percentage of summer crashes related to rear-end crashes at or approaching an intersection.

Traffic analysis can be found in Appendix D.

12.0 SAFETY IMPROVEMENTS

The new alignment will provide a geometric improvement, namely horizontal, which will allow traffic to safely maintain the posted speed limit of 55 mph. The realignment of the curve and the addition of turning lanes at both intersections is aimed at reducing the current crash rates within the project limits. The addition of turning lanes is in response to many crashes during summer months (May thru September) that have resulted in a rear-end collision. Furthermore, a larger radius of curvature, and a proper superelevation, will provide traffic to safely navigate the corridor during winter months (October thru April) when the road conditions are below optimal.

13.0 RIGHT-OF-WAY REQUIREMENTS

The Seward Highway – Portage Curve Project will require the acquisition of additional right-of-way (ROW).

Seward Highway MP 75-90 – Portage Curve 6 Design Study Report

Beginning at station 26+00 the preferred alignment diverts from the existing alignment. The preferred alignment crosses into Chugach State owned land which will require a full acquisition. Any privately- owned land along the preferred alignment will need to be bought out.

The Portage-Glacier Road will be extended to meet the preferred alignment, and this will require no additional ROW. The extension is built of the road will extend into land currently owned by the Alaska DOT&PF.

14.0 PEDESTRIAN AND BICYCLE FACILITIES

There are no separated pedestrian and bicycle accommodations within the project limits. Pedestrians and bicycles may use the new shoulders of the highway. Future designs should accommodate a pedestrian underpass on both the Portage Creek #1 and Placer River bridges.

15.0 UTILITY RELOCATION AND COORDINATION

Utility companies with facilities in the project limits include General Communications Inc. (GCI) and Chugach Electric. Utilities will require relocation and agreements will need to be developed, at select locations throughout the project, to address the following conflicts:

15.1 GCI

There will be several conflicts with GCI’s fiber optic cables in the area which includes issues during reconstruction of the Alaska Wildlife Conservation Center Road from Sta. 0+50 to 1+00. Additionally, there will be more conflicts along the realignment of the Seward Highway from Sta. 29+00 to 31+00 and Sta. 38+00 to 42+00. GCI also owns an underground telephone line in the area which will have a conflict from Sta. 31+00 to 32+00, and a telephone pole will need relocation at Sta. 32+00.

15.2 Chugach Electric

Overhead electricity lines will need to be relocated due to the realignment of the Seward Highway at Sta. 35+50 and 56+00, as well as from Sta. 63+00 to 64+00.

16.0 PRELIMINARY WORK ZONE TRAFFIC CONTROL

The HPCM, Section 1400.2 sets forth the criteria for determining if a project is ‘significant’ for purposes of determining the level of effort required in developing a Traffic Management Plan (TMP). Significant projects fall into either a Category 1 or Category 2 classification.

Category 1:

Project occupies a location for more than three days with either intermittent or continuous lane closures on Interstate Highways within a Transportation Management Area – Criteria Not Met

Category 2:

Project occupies a location for more than three days with either intermittent or continuous lane closures on arterials, expressway, or freeways with Annual Average Daily Traffic (AADT) of 30,000 or more – Criteria Not Met

Seward Highway MP 75-90 – Portage Curve 7 Design Study Report

Project fully closes an arterial for more than one hour at a time with no practical alternate route – Criteria Not Met

Any 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 Not Met

The HPCM, Section 1400.2 sets forth the criteria for determining if a project is to be classified as a “Significant Project” for purposes of determining the level of effort required in developing a TMP. Though the project is classified as a Rural Other Principal Arterial, the project is not located within the Anchorage urban area, roadway AADTs are below 30,000 vpd, and in the event of a full closure a practical alternate route is not available. Therefore, the project is not considered a “Significant Project.”

16.1 Traffic Control Plan (TCP)

The contractor will develop a TCP during construction, to safely guide and protect the traveling public in work zones, in accordance with the ATM and the project specifications. The plan will be assessed and approved by the Construction Project Engineer and the Traffic Control Engineer. The contractor is responsible for providing advanced 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 disseminate information include:

 Contractor’s Worksite Traffic Supervisor  Department’s Construction section thru the Department’s 511 system  Department’s Navigator website  Television, Radio, and/or newspaper  Other location-specific communication tools

The traveling public should not be caught unaware by any closures, detours, delays, night work, or any potentially disruptive activity.

16.3 Transportation Operations Plan (TOP)

The Department will coordinate with relevant public agencies and event organizers, and incorporate means and methods for minimizing traffic impacts with the contractor not covered by the TCP or the PIP within the project plans.

17.0 STRUCTURAL SECTION AND PAVEMENT DESIGN

Pavement recommendations are being developed; however, based on other recent projects in the area, preliminary recommended sections are:

Seward Highway MP 75-90 – Portage Curve 8 Design Study Report

Seward Highway Typical: 2” HMA Type II, PG 58-34 3” ATB, PG 58-34 2” D-1 36” Selected Material, Type A

Portage-Glacier Road Typical: 2” HMA Type II, PG 58-34 3” ATB, PG 58-34 2” D-1 36” Selected Material, Type A

Alaska Wildlife Conservation Center Entrance Typical: Match existing

Geotechnical recommendations and potential material source information are provided in Appendix C.

18.0 COST ESTIMATE

The project cost estimate was based on the calculation of expected pay items related to the roadway and bridge. Preliminary Engineering was taken as 8% of the total budget and both Right-of-Way and Utility Relocation was taken as 5%.

The project cost estimate is as follows:

Preliminary Engineering $ 2,400,000

Right-of-Way $ 1,500,000

Utility Relocation $ 1,500,000

Construction $ 30,000,000

Total $ 35,400,000

19.0 ENVIRONMENTAL COMMITMENTS AND CONSIDERATIONS

At this point in the design process, the Seward Highway Milepost 78-79 Rehabilitation Project is under local review for the purposes of this design study report. Therefore, the environmental impact considerations are rudimentary in nature. The preliminary factors being considered are the required environmental permits that will potentially need to be applied for and the immediate impact on the surrounding environment.

Given the surrounding wetland limits, it was determined that the project will be located entirely on wetlands. Consequently, the current local review design study report presents an estimated area of environmental impact from the project on the wetlands. This area was found to be about 10 acres of wetland impacts. Future considerations must be based on a more in depth analysis than this.

Additionally, it was also found that the following permits, per the Alaska Highway Drainage Manual, will likely be required for the project:

Seward Highway MP 75-90 – Portage Curve 9 Design Study Report

 Section 404 Permit – (U.S. Army Corps of Engineers)  Section 10 Permit – (U.S. Army Corps of Engineers)  Land Use Permit – (Alaska Department of Natural Resources)  Temporary Water Use Permit – (Alaska Department of Natural Resources)  Fish Habitat Permit (Title 41) – (Alaska Department of Natural Resources)  National Pollution Discharge Elimination System Permit (NPDES) – (U.S. Environmental Protection Agency)  401 Certificate of Reasonable Assurance – (AK Dept. of Environmental Conservation)  Section 106 Review – (AK Dept. of Natural Resources, State Historic Preservation Office)  Endangered Species Act of 1973, Section 7 Consultation – (U.S. Fish and Wildlife Service or National Marine Fisheries Service)  Marine Mammal Protection Act Consultation - (National Marine Fisheries Service)  Section 9 Permit for Bridges Over Navigable Waters – (U.S. Coast Guard)

The contractor is responsible for obtaining all necessary permits and clearances for materials sites, disposal sites, and staging areas unless DOT&PF has obtained all necessary permits.

The contractor will be required to prepare and implement a SWPPP that conforms to the DOT&PF BMPs for erosion and sediment control in accordance with the DOT&PF contract specifications. Appropriate erosion and siltation controls will be used and maintained in optimal condition during construction and all other exposed soils/fills will be permanently stabilized.

The contractor will be required to dispose of solid waste at an ADEC approved landfill. An ESCP will be made available to the contractor to use as guidance in developing the SWPPP.

20.0 BRIDGES

Two significant bridges will be constructed to span Portage Creek #1 and Placer River. The Portage Creek #1 bridge will be approximately 350 feet in length and Placer River will be approximately 650 feet in length. Both bridge elevations must accommodate the 100-year flood event for the respective rivers they span. More information is provided in Appendix F.

21.0 EXCEPTIONS TO DESIGN STANDARDS

There are no exceptions to design standards for this project.

22.0 MAINTENANCE CONSIDERATIONS

Maintenance will remain the responsibility of the State of Alaska and the local DOT&PF Maintenance and Operations Station located in Girdwood, AK.

23.0 ITS FEATURES

There are no ITS features incorporated into the proposed project.

Seward Highway MP 75-90 – Portage Curve 10 Design Study Report

Seward Highway MP 75-90 – Portage Curve Design Study Report

APPENDIX A

Approved Design Criteria And Design Designation

Seward Highway MP 75-90 – Portage Curve Design Study Report

Project Design Criteria Project Name: Seward Highway MP 75-90 - Portage Curve  New Construction/Reconstruction* 3R PM Other: Project Number: NHS Non NHS Functional Classification: Rural Interstate Source/Comments Design Year: 2037 Present ADT: 4224 Design Year ADT: 6037 Mid Design Period ADT: DHV: 23.6 Directional Split: 48/52 Percent Trucks: 13.9 Equivalent Axle Loading: Pavement Design Year: 2037 Design Vehicle: WB-109D Terrain: Flate Number of Roadways: 1 Design Speed: 60 mph Width of Traveled Way: 24 feet Width of Shoulders: Outside: 8 feet Inside: 8 feet Cross Slope: 2% Superelevation Rate: 6% Max Minimum Radius of Curvature: 1838 feet Minimum K-Value for Vertical Curves: Sag:136 Crest: 1628 Maximum Allowable Grade: 6% Minimum Allowable Grade: 0.50% Stopping Sight Distance: 570 feet Lateral Offset to Obstruction: N/A Vertical Clearance: 16 feet Bridge Width: 40 feet Bridge Structural Capacity: HS-25 Passing Sight Distance: 2135 feet Surface Treatment: T/W: HMA Shoulders: HMA Side Slope Ratios: Foreslopes:4(H):1(V) Backslopes: 6(H):1(V) Degree of Access Control: Median Treatment: N/A Illumination: N/A Curb Usage and Type: N/A Bicycle Provisions: N/A Pedestrian Provisions: N/A Misc. Criteria:

Proposed - Designer/Consultant: Date: Endorsed - Engineering Manager: Date: Approved - Preconstruction Engineer: Date:

Shaded criteria are commonly referred to as the FHWA 13 controlling criteria . *For NHS routes only, these criteria must meet the minimums established in the Green Book (AASHTO A Policy on Geometric Design of Highway and Streets ). For all other routes, these criteria must meet the minimums established in the Alaska Highway Preconstruction Manual . Otherwise a Design Exception must be approved.

Design Criterion marked with a "#" do not need to meet minimums and have a Design Exception(s) and/or Design Waiver(s) approved. See the approved DSR for Design Exception/Design Waiver approval(s) and approved design criteria values.

Seward Highway MP 75-90 – Portage Curve Design Study Report

Seward Highway MP 75-90 – Portage Curve Design Study Report

APPENDIX B

Typical Sections

Seward Highway MP 75-90 – Portage Curve Design Study Report

Seward Highway MP 75-90 – Portage Curve Design Study Report

APPENDIX C

Material and Geotechnical Recommendations

Seward Highway MP 75-90 – Portage Curve Design Study Report

Material Recommendations Report

Seward Highway Milepost 75-90 Rehabilitation Project Portage Curve Project No.: OA3/58105 Group D

Prepared For: State of Alaska Department of Transportation and Public Facilities 4111 Aviation Avenue Anchorage, Alaska 99519

Prepared By: Seawolf Engineering 2900 Spirit Drive, Room 205 Anchorage, AK 99508

Author:

Zach Cuddihy

Seward Highway MP 75-90 – Portage Curve ii Design Study Report

Table of Contents 1.0 Introduction ...... 1 Project Description ...... 1 2.0 Climate ...... 1 3.0 Recommendations ...... 1 3.1 Earthwork ...... 2 3.2 Structural Pavement Section ...... 2 3.3 Material Sources ...... 2 4.0 Estimated Settlement ...... 2

Seward Highway MP 75-90 – Portage Curve i Design Study Report

Figures

Figure 1: Average Temperatures….………………………..…………….……………………….1

Tables

Table 1: Estimated Primary Settlement….………………………..…………….……………………3

Seward Highway MP 75-90 – Portage Curve ii Design Study Report

1.0 Introduction

This report presents the preliminary results of an on-going geotechnical investigation performed for the Seward Highway MP 75-90: Portage Curve project. In general, the purpose of this investigation was to evaluate the existing subsurface conditions and to provide geotechnical recommendations for the further design of this project. Recommendations are based off the boring test reports gathered during a field exploration done by Shannon and Wilson, Inc. in November and December of 2014, and in May of 2015.

1.1 Project Description

The preferred alignment for the Portage Curve project diverts from the existing alignment and into land classified as wetlands. The geotechnical sight visit that was completed indicated that more than 60% of the soil along the preferred alignment contains silt or silty sand. Additionally, groundwater is routinely found near the surface.

2.0 Climate

Climate data was obtained from Alyeska Resort in Girdwood, AK. Average temperatures during winter months (October thru April) were consistently near or below 32 degrees. These ambient temperatures coupled with moisture content, soil type and ground water directly impact the depth of freeze.

Figure 1. Average Temperatures

3.0 Recommendations

Based on the geotechnical site visit and soil test reports provides by Shannon and Wilson, Inc., specific recommendations regarding earthwork and structural pavement sections are provided below.

3.1 Earthwork

Borings along the proposed alignment indicate the existing soils near the surface are mainly comprised of silts with depths in excess of approximately 15 feet. Silt is classified as a frost susceptible soil due to the high amount of fines (P200s). In addition, the ground water table is consistently within five feet of the surface, if not at surface level. Lastly, from the boring logs it was indicated that silt near the surface was classified as “loose to very loose” due to the low blow count values (<5). As such, long term settlement and consistent freeze-thaw cycles pose a risk to the structural pavement section.

Seward Highway MP 75-90 – Portage Curve 1 Design Study Report

It is recommended that the silt beneath the preferred alignment be excavated and filled with Type C material. This is discussed in more depth in the following section.

3.2 Structural Pavement Section

The structural pavement sections were based on projects in the vicinity. These are preliminary estimates to use for design purposes, but a proper materials testing

Seward Highway MP 78-79:

 2” Type II HMA, PG 58-34  STE-1 Asphalt for Tack Coat  3” ATB, PG 58-34  2” D-1  36” Selected Material, Type A

Portage-Glacier Road:

 2” Type II HMA, PG 58-34  STE-1 Asphalt for Tack Coat  3” ATB, PG 58-34  2” D-1  36” Selected Material, Type A

Alaska Wildlife Conservation Center Road:

 Match existing

3.3 Material Sources

No material source investigations were performed for this project as all materials are expected to come from contractor supplied sources.

4.0 Estimated Settlement

Utilizing data from the boring test reports, approximate settlement values were calculated using elementary consolidation analysis. This was aimed at determining if the existing soil was suitable for a roadway embankment to be constructed without excavation of any soil. The assumption in the calculations is that fill would be placed on the existing ground to bring it up to the required elevation for the structural pavement section to be built; this was denoted as the “surcharge settlement”.

Estimated settlement analysis was done on borings TH14-034, TH15-040, and TH14-044. The boring test reports can be found in Appendix A.

Seward Highway MP 75-90 – Portage Curve 2 Design Study Report

Table 1. Estimated Primary Settlement Test Hole # TH14-034

Sample Soil Sc,total # Type Sc,theoretical (in) Sc,surcharge (in) Sc,pavement (in) (in) % Surcharge 1 ML 2.094 2.571 0.137 2.708 95% 2 ML 1.119 1.484 0.131 1.614 92% 3 ML 0.944 1.305 0.143 1.447 90% 4 ML 0.531 0.753 0.091 0.844 89% 5 SP 0.292 0.423 0.053 0.476 89% 6 SP 0.285 0.421 0.063 0.483 87% Total: 7.573 92% Test Hole # TH15-040

Sample Soil Sc,total # Type Sc,theoretical (in) Sc,surcharge (in) Sc,pavement (in) (in) % Surcharge 1 ML 2.784 3.549 0.273 3.822 93% 2 ML 1.192 1.642 0.203 1.845 89% 3 ML 1.287 1.856 0.266 2.122 87% 4 ML 0.218 0.322 0.055 0.377 86% Total: 8.165 90% Test Hole # TH14-044

Sample Soil Sc,total # Type Sc,theoretical (in) Sc,surcharge (in) Sc,pavement (in) (in) % Surcharge 1 ML 2.120 2.596 0.156 2.753 94% 2 ML 1.142 1.509 0.143 1.652 91% 3 ML 1.252 1.736 0.206 1.941 89% 4 ML 0.296 0.419 0.030 0.449 93% 5 SP 0.259 0.372 0.046 0.418 89% 6 SP 0.473 0.693 0.075 0.768 90% Total: 7.981 93%

The unit weights of the pavement structure were assumed as followed:

 HMA = 145 lbs/ft3  ATB = 145 lbs/ft3  D-1 = 125 lbs/ft3  Select Type A = 125 lbs/ft3  Fill (Surcharge Soil) = 125 lbs/ft3

When the pavement structure is constructed, the total load placed onto the existing ground would be ~850 lbs/ft3. If this pavement structure is built without placing the additional fill then the theoretical values in column three would be the expected, immediate settlement. The long-term settlement from this loading would be of a much higher concern because the silty soils have a moisture content in excess of 30%. The amount of time for this water to escape the soil could be years because silt has a very low hydraulic conductivity.

Seward Highway MP 75-90 – Portage Curve 3 Design Study Report

Due to the effects of long term settlement, leaving the silt in-place could cause excessive settlement that is not accounted for in the above tables. As such, it is recommended to excavate the silt where it is possible. The excavation should be backfilled with Type C material to bring it back to existing surface level before placing the embankment and pavement structure.

Seward Highway MP 75-90 – Portage Curve 4 Design Study Report

Appendix A

Boring Test Reports

Seward Highway MP 75-90 – Portage Curve 5 Design Study Report

Seward Highway MP 75-90 – Portage Curve 6 Design Study Report

Seward Highway MP 75-90 – Portage Curve 7 Design Study Report

Seward Highway MP 75-90 – Portage Curve 8 Design Study Report

Seward Highway MP 75-90 – Portage Curve 9 Design Study Report

Seward Highway MP 75-90 – Portage Curve Design Study Report

APPENDIX D

Traffic Analysis

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)

Seward Highway MP 75-90 – Portage Curve Design Study Report

Traffic Analysis Report

Seward Highway Milepost 75-90 Rehabilitation Project Portage Curve Project No.: OA3/58105 Group D

Prepared For: State of Alaska Department of Transportation and Public Facilities 4111 Aviation Avenue Anchorage, Alaska 99519

Prepared By: Seawolf Engineering 2900 Spirit Drive, Room 205 Anchorage, AK 99508

Author:

Zach Cuddihy

Seward Highway MP 75-90 – Portage Curve Design Study Report

Table of Contents

1.0 Introduction ...... 1 1.1 OBJECTIVE ...... 1 2.0 Existing Conditions ...... 1 2.1 DESIGN YEAR CONDITIONS ...... 2 3.0 Crash Data Analysis ...... 2 3.1 INTERSECTION CRASH HISTORY AND ANALYSIS ...... 3 3.2 SEGMENT CRASH HISTORY AND ANALYSIS ...... 3 3.3 CRASH DATA CONCLUSIONS ...... 6 4.0 Intersection Analysis ...... 6 4.1 SUMMARY OF TURNING MOVEMENTS ...... 6 4.2 STORAGE LENGTH FOR TURN LANES ...... 7

Seward Highway MP 75-90 – Portage Curve Design Study Report

Figures

Figure 1: Traffic Data…………………………………………………..…………………………1 Figure 2: Intersection Crash Data Collison Type……………………..……………..……………2 Figure 3: Intersection Crash Data Severity....…………..…………………………………………3 Figure 4: Segment Crash Data Collision Type……………………………………………………4 Figure 5: Segment Crash Data Severity...…………………………………………………………5 Figure 6: Segment Road Conditions: Winter Crashes..…………………………………………5

Tables

Table 1: Summary of Turning Movements at Wildlife Center………..…………………..………6 Table 2: Peak Hourly Turning Volumes at Wildlife Center…………..…………………..………7 Table 3: Percentage of Vehicles Turnings at Wildlife Center.………..…………………..………7 Table 4: Calculation of 95th Percentile Queue……………….………..…………………..………8

Appendices

Appendix A………….………..………………...……..……...…….……Turning Movements Plot

Seward Highway MP 75-90 – Portage Curve ii Design Study Report

1.0 Introduction

The Seward Highway serves to connect the Anchorage Bowl to the Kenai Peninsula. Despite being an interstate where the speed limit can range from 55 mph to 65 mph, there are still several intersections along the highway where no turn lanes are provided. There are two of these types of intersections between MP 78 and 79 along the Portage Curve. Additionally, traffic flow varies with the seasons which adds additional demand on the Seward Highway during peak summer weekends.

1.1 Objective

This report documents and summarizes the traffic analysis done for the Portage Curve between Mileposts (MP) 78 and 79. Objectives of this analysis are:

 Project existing traffic data to the design year of 2037  Evaluate crash history information to determine possible causes of vehicular crashes  Analyze existing intersection conditions and project possibilities for future design

Throughout this report for the Portage Curve project, any analyses done will conform to DOT&PF HPM and AASHTO Green Book standards.

2.0 Existing Conditions

Existing traffic volumes were obtained from a DOT&PF study conducted in 2013; this data can be seen in Figure 1. The average daily traffic (ADT) for 2013 was 3,934 with a compound growth rate of 1.08% per year. However, summer and winter months vary drastically in terms of traffic volumes. During peak weeks in the summer the ADT can exceed 10,000.

Figure 1. Traffic Data

Seward Highway MP 75-90 – Portage Curve 1 Design Study Report

2.1 Design Year Conditions

A design year of 2037 is being used for the purpose of this report. Projecting the ADT to that year yields a value of approximately 6,000. The Design Hourly Volume (DHV) and Peak Hour Factor were assumed to stay constant through the design year for the purposes of this report.

3.0 Crash Data Analysis

Crash data information was obtained from the Alaska DOT&PF for the timeframe of 1999 to 2008. The information is split into two distinct types, intersection and segment crashes. Crashes that are identified as intersection crashes had the follow criteria: vehicles approaching an intersection, vehicles slowing at an approach to an intersection and vehicles in the act of a turning movement. Crashes that are classified as a segment crash is identified as a crash not in the vicinity of an intersection.

3.1 Intersection Crash History and Analysis

This analysis was used to determine the most common crash types, the crash rate for the Portage- Glacier Road intersection, and to compare the calculated crash rate with DOT&PF average crash rates. The only classified intersection crashes for this project location were crashes that occurred at the Portage-Glacier Road intersection. A total of 10 reported crashes were logged for this intersection, and no fatalities were recorded. A summary of the crash history and crash severity can be seen in Figure 1 and Figure 2.

Intersection Collision Type Ditch 10% Rear-End 20%

Angle 10%

Object Animal 50% 10%

Figure 2. Intersection Crash Data Collision Type

Seward Highway MP 75-90 – Portage Curve 2 Design Study Report

Intersection Collision Severity

Possible Injury 20%

Property Damage Only 80%

Figure 3. Intersection Collision Data Severity

Intersection crash rates are expressed as crashes per million entering vehicles (MEV). To calculate intersection crash rates, the following equation was used:

∗ 1,000,000/ ∗365∗

An intersection crash rate of 0.76 was calculated for the Portage-Glacier Road intersection using the following parameters for the crash rate formula:

 Total Crashes = 10  AADT = 4,000  Years = 9

The approximate statewide average crash rate for a two-way stop intersection with 10 conflicts is 0.60 (AK DOT&PF 2009-2011 Statewide Crash Rates at Intersections by Number of Conflicts). This intersection exceeds the statewide average crash rate.

3.2 Segment Crash History and Analysis

Any crash not characterized as an intersection crash was defined as a segment crash. Crashes at the Alaska Wildlife Conservation Center intersection was not defined as an intersection crash, therefore, any crash at that intersection was included in the segment crash history. A total of 22 crashes were reported between MP 78 and 79, and no fatalities were recorded. A summary of the collision type, collision severity and environmental conditions can be found in Figures 3 – 5.

The collision type and environmental conditions were evaluated to identify if there are any deficiencies with the existing roadway design.

Seward Highway MP 75-90 – Portage Curve 3 Design Study Report

Segment crash rate is similar to the intersection crash rate; however, it takes into account the total length of the segment. Segment crashes are expressed as crashes per million vehicle miles (MVM). The following equation is used to analyze the segment crash rate:

∗ 1,000,000/ ∗365∗ ∗

A crash rate of 1.67 MVM was calculated for the Portage Curve segment from MP 78-79 using the following parameters:

 Total crashes = 22  AADT = 4,000  Segment Length = 1 mile  Number of Years = 9

The approximate statewide average crash rate for an Undivided Rural Interstate is 1.0 MVM (AK DOT&PF 2009-2011 Statewide Segment Crash Rates by Road Category). This segment exceeds the crash rate for an undivided rural interstate.

Segment Crash Type Other 9% Angle 5% Rear-End 32% Animal 9%

Ditch 4%

Ran Off Road 9%

Object 32% Figure 4. Segment Crash Type

Seward Highway MP 75-90 – Portage Curve 4 Design Study Report

Segment Crash Severity Major Injury 9%

Minor Injury 23%

Property Damage Only 68%

Figure 5. Segment Crash Data Severity

Segment Road Conditions: Winter Collisions

Missing 10%

Dry 10%

Slush Ice 10% 50%

Snow 20%

Figure 6. Segment Road Conditions: Winter Collisions

Seward Highway MP 75-90 – Portage Curve 5 Design Study Report

A winter crash is classified as a crash occurring between the months of October and April. There was a total of 10 segment crashes recorded during these months between 1999 and 2008. Every one of these crashes accounts for all the crashes classified as Animal, Object or Ditch in Figure 3.

3.3 Crash Data Conclusions

An analysis of the crash data from 1999-2008 indicated the following observations. Design team recommendations are shown in italics.

 The crash rate for the Portage-Glacier Road intersection exceeds the DOT&PF’s average crash rate for a two-way stop intersection. A re-designed intersection with dedicated turn lanes for north and south bound traffic could improve current conditions.  Winter month segment crashes were due to below optimal road conditions and resulted in crashes with objects and animals, or resulted in the vehicle running off the road. The existing curve does not meet the minimum radius of curvature for a 65mph design speed, realignment of the curve will improve the mobility in this corridor.

4.0 Intersection Analysis

Turning movements were obtained from the DOT&PF and were observed for the Alaska Wildlife Conservation Center for 6/20/2013 to 6/23/2013. No turning movements were obtained for the Portage- Glacier Road intersection so it was assumed that the turning movements would be double for that intersection. Turning movement data can be found in Appendix A.

4.1 Summary of Turning Movements

Table 1 summarizes all the turning and through movements recorded at the Alaska Wildlife Conservation Center intersection.

Table 1. Summary of Turning Movements at Wildlife Center Day Summary Northbound Vehicles Southbound Vehicles Wildlife Center Turn Turn Day Turn Left Straight Total Turn Right Straight Total North South 6/20/2013 133 2636 2769 184 3020 3204 181 127 6/21/2013 161 3012 3173 249 4615 4864 244 161 6/22/2013 167 3928 4095 259 4613 4872 247 170 6/23/2013 138 4598 4736 303 3118 3421 187 206 Total 599 14174 14773 995 15366 16361 859 664

Each row summarizes a full days’ worth of turning movements, even during hours where traffic volumes are low. Overall turning volumes are considerably low when compared to the total volume of vehicles passing through the intersection. Approximately 5% of the total vehicles were turning into or out of the Wildlife Center during the observed time. Turning movements for peak hours were noted and analyzed in Table 2 and 3.

Seward Highway MP 75-90 – Portage Curve 6 Design Study Report

Table 2. Peak Hourly Turning Volumes at Wildlife Center Peak Hourly Data Northbound Vehicles Southbound Vehicles Wildlife Center Time Observed Turn Turn Turn Turn Left Straight Total Right Straight Total North South Start Finish 10:45:00 11:45:00 6/20/2013 14 160 174 21 302 323 6 11 AM AM 4:30:00 5:30:00 6/20/2013 17 303 320 10 287 297 25 13 PM PM 11:00:00 12:00:00 6/21/2013 11 238 249 32 322 354 19 13 AM PM 6:15:00 7:15:00 6/21/2013 4 364 368 9 511 520 20 11 PM PM 11:00:00 12:00:00 6/22/2013 19 254 273 32 519 551 18 20 AM PM 1:30:00 2:30:00 6/22/2013 11 359 370 37 547 584 31 37 PM PM 11:00:00 12:00:00 6/23/2013 17 395 412 58 364 422 6 21 AM PM 3:30:00 4:30:00 6/23/2013 21 680 701 34 354 388 36 27 PM PM

Table 3. Percentage of Vehicles Turning at Wildlife Center Northbound Southbound Day Day % Hour 1 % Hour 2 % % Hour 1 % Hour 2 % 6/20/2013 5% 8% 5% 6% 7% 3% 6/21/2013 5% 4% 1% 5% 9% 2% 6/22/2013 4% 7% 3% 5% 6% 6% 6/23/2013 3% 4% 3% 9% 14% 9% Average 4% 6% 3% 6% 9% 5%

During peak hours, generally 11:00 AM and 5-6:00 PM, turning movements did not see a substantial increase. There were fluctuations which saw a max of 14% of vehicles turning and a minimum of 1% of vehicles turnings. However, the peak hour turning movements generally averaged out to ~5%. As such, a turning rate of 5% of vehicles for the Wildlife Center and 10% of vehicles for the Portage-Glacier Road intersection will be used.

4.2 Storage Length for Turn Lanes

An important aspect outlined in section 3.2 Crash Data Conclusions stated that turn lanes should be added for both intersections. Total length of turn lanes will be decided by the following factors: storage length and deceleration time. The storage length is dependent on traffic data whereas the deceleration length is dependent on vehicular properties. Estimation of storage length, also known as queue length, is an important consideration for an unsignalized intersection such as the one at Portage-Glacier Road.

Seward Highway MP 75-90 – Portage Curve 7 Design Study Report

The Highway Capacity Manual 2000 outlines the procedure for estimating the queue length at an unsignalized intersection by the following equation:

3600 , , , 900 ∗ ∗ 1 ∗ , 150 ∗ 3600 Variable Definitions:

th Q95 = 95 -percentile queue (veh) vx = flow rate for movement (veh/h) Cm,x = potential capacity of movement (veh/h) T = analysis of time period (h) (T=0.25 for a 15-min period)

Table 4. Calculation of 95th-percentile queue for Portage-Glacier Road Intersection 2037 ADT: 6036 veh DHV: 23.6% % Vehicles Turning: 10% Direction Distribution: 48/52 (S/N)

Max Hourly Volume: 1424 veh/hr Total Vehicles Turning: 142 veh/hr Left Turning Vehicles, vx: 68 veh/hr

Base Critical Gap 4.1 s Base Follow-up 2.2 s

Critical Gap 4.239 s Follow Up Time 2.3251 s

Potential Capacity, Cmx 814 veh/hr

95th % Queue 0.274 veh

The estimated storage length for a left-hand turn lane at the Portage-Glacier Road intersection is ~0.27 vehicles. As such, the storage length should be assumed as one vehicle length while the total length of the turn lane will largely depend on the deceleration of a single design vehicle. The intersection at the Wildlife Center will have a queue length similar to the one in Table 4 so the deceleration length will control the turn lane.

Seward Highway MP 75-90 – Portage Curve 8 Design Study Report

APPENDIX A

Turning Movements Plots

Seward Highway MP 75-90 – Portage Curve 9 Design Study Report

Seward Highway MP 75-90 – Portage Curve 10 Design Study Report

Seward Highway MP 75-90 – Portage Curve 11 Design Study Report

Seward Highway MP 75-90 – Portage Curve 12 Design Study Report

Seward Highway MP 75-90 – Portage Curve 13 Design Study Report

Seward Highway MP 75-90 – Portage Curve 14 Design Study Report

Seward Highway MP 75-90 – Portage Curve 15 Design Study Report

Seward Highway MP 75-90 – Portage Curve 16 Design Study Report

Seward Highway MP 75-90 – Portage Curve 17 Design Study Report

Seward Highway MP 75-90 – Portage Curve 18 Design Study Report

Seward Highway MP 75-90 – Portage Curve 19 Design Study Report

Seward Highway MP 75-90 – Portage Curve 20 Design Study Report

Seward Highway MP 75-90 – Portage Curve 21 Design Study Report

Seward Highway MP 75-90 – Portage Curve 22 Design Study Report

Seward Highway MP 75-90 – Portage Curve 23 Design Study Report

Seward Highway MP 75-90 – Portage Curve 24 Design Study Report

Seward Highway MP 75-90 – Portage Curve 25 Design Study Report

Seward Highway MP 75-90 – Portage Curve Design Study Report

APPENDIX E

Hydrologic and Hydrologic Report

Seward Highway MP 75-90 – Portage Curve Design Study Report

Hydraulic and Hydrologic Report

Seward Highway Milepost 75-90 Rehabilitation Project Portage Curve Project No.: OA3/58105

Group D

Prepared For: State of Alaska Department of Transportation and Public Facilities 4111 Aviation Avenue Anchorage, Alaska 99519

Prepared By: Seawolf Engineering 2900 Spirit Drive, Room 205 Anchorage, AK 99508

Author:

Grant Warnke

April 2017

Seward Highway MP 75-90 – Portage Curve Design Study Report

Table of Contents Table of Figures...... ii Notation/Acronyms ...... iii Introduction ...... 1 Objective ...... 1 Project Description ...... 1 Hydraulic and Hydrologic Analysis ...... 2 Flood Risk ...... 2 Drainage Area Characteristics ...... 2 Methodology ...... 4 Design Criteria ...... 4 Bridge Clearances – Regression Analysis ...... 4 Culvert Design – Rational Method ...... 6 Results ...... 7 Bridge Clearances – Regression Analysis ...... 7 Culvert Design – Rational Method ...... 8 Limitations ...... 11 Bridge Clearances – Regression Analysis ...... 11 Culvert Design – Rational Method ...... 11 Recommendations ...... 12 Equations ...... 13 Works Cited ...... 13 Miscellaneous Design Criteria ...... 14

Seward Highway MP 75-90 – Portage Curve i Design Study Report

Table of Figures Figure 1. Portage Creek & Placer River Drainage Basins...... 1 Figure 2. A: Top Left; B: Top Right; C: Bottom Left; D: Bottom Right; E: Portage Rd...... 2 Figure 3. Portage Creek Cross Section ...... 5 Figure 4. Placer River Cross Section ...... 5 Figure 5. Flow Type Classification (AHDM Chapter 9) ...... 9 Figure 6. IDF Curves ...... 9 Figure 7. Channel Cross Section Properties, from Open Channel Hydraulics (Strum) ...... 12 Figure 8. Appendix A, Chapter 7 of AHDM ...... 14 Figure 9. Appendix A, Chapter 9 of AHDM ...... 14 Figure 10. Appendix D, Chapter 7 of AHDM ...... 15 Figure 11. Appendix D, Chapter 7 of AHDM ...... 15 Figure 12. Head Loss Formulas from Chapter 9 of AHDM ...... 16 Figure 13. Table 2 In Appendix A of Chapter 9 of AHDM ...... 17 Figure 14. Runoff Coefficients for Rational Method Provided by ODOT Hydraulic Manual ...... 18 Figure 15. Runoff Coefficient Adjustment Factors from ODOT Hydraulic Manual ...... 18

Table 1. Drainage Basin Characteristics ...... 2 Table 2. Storm Runoff Drainage Basins ...... 3 Table 3. Peak Flow Rates for Portage Creek Using Regression Analysis ...... 7 Table 4. Peak Flow Rates for Placer River Using Regression Analysis ...... 7 Table 5. Peak Flow Elevations ...... 8 Table 6. Determination of Peak 100-Year Storm Flow ...... 10 Table 7. 36" CSP Design Check & Flow Classification ...... 10 Table 8. Determination of Head Loss & Tail Water Effects ...... 11

Seward Highway MP 75-90 – Portage Curve ii Design Study Report

Notation/Acronyms

AASHTO…………………….…… American Association of State Highway and Transportation Officials AHDM………………………………….……………………………… Alaska Highway Drainage Manual AKDOT………………………………………………………………Alaska Department of Transportation FEEMA…………………………………………………………. Federal Emergency Management Agency NOAA…………………………..………………………... National Oceanic and Atmospheric Association ODOT……………………...………………………………………..… Ohio Department of Transportation USGS…………………….………………………………………………. United States Geological Survey

Seward Highway MP 75-90 – Portage Curve iii Design Study Report

Introduction

Objective

The primary objective of this study is to identify the clearance needed for the bridges on the project based on a hydrologic and hydraulic analysis of the waterways underneath the bridges. The bridge clearance solution will require research of different methods presented in the Alaska Highway Drainage Manual (Alaska Highway Drainage Manual, 2006).

The secondary objective is to propose a design for a general culvert to be placed in and around the project area. The proposed culvert must be designed as an adequate drainage system for storm water runoff as to avoid saturation issues to our proposed corridor. This will help to mitigate issues involving the structural integrity of the subgrade below the proposed road.

This study provides an overview of said methods, design requirements, and a final solution for each problem. All design guidelines and calculations are in accordance with the Alaska Highway Drainage Manual, which itself is based on the Model Drainage Manual written by the AASHTO Task Force on Hydrology and Hydraulics.

Project Description

This hydrologic and hydraulic report was prepared in support of the Seward Highway Milepost 75-90 Rehabilitation Project. More specifically, it was developed for the milepost 78-79 portion of the project. The proposed road alignment will help mitigate crashes at the sharp curve at Portage Glacier Road, while also avoiding four cultural sites surrounding the area and minimizing environmental impacts in the surrounding area. Additionally, the new alignment will minimize right of way acquisition from the Chugach Forest and private parties.

The new corridor will have an increased radius on the Portage Curve to smooth out the curve and make it more drivable. The purpose of this is to increase the safety of the current sharp curve while maintaining the current design speed. Current traffic data indicates that the design speed is too high for the current curve alignment, especially in winter conditions. The redesigned intersection at Portage Glacier Road will also encourage fluid motions onto and off the Seward Highway. This will alleviate congestion at the current turn pockets and mitigate rear end collisions.

In addition to the road rehabilitation and realignment, the Portage Creek and Placer River bridges will be replaced due to being structurally deficient. Both these bridge decks were rated below a four, and have numerous areas of rusting and exposed rebar on the bridge deck. The proposed bridge designs will be very similar to current conditions. However, they will insure a smooth transition from the roads and minimize environmental impacts to the waterways they pass over.

Many aspects of this design require hydraulic and hydrologic considerations. Therefore, a simple analysis was conducted for the area.

Seward Highway MP 75-90 – Portage Curve 1 Design Study Report

Hydraulic and Hydrologic Analysis

Flood Risk

The Federal Emergency Management Agency classifies the project area (Map #020005, Panel 1755D) as Zone X. This necessitates areas outside of the 0.2% annual chance flood (500-Year Storm), but still susceptible to flooding. Per Appendix A in the Alaska Highway Drainage Manual, culverts and bridges in designated flood areas are to be designed with a return period of 100 years. Therefore, the culverts and bridges were designed in accordance with the 1% annual exceedance probability.

Drainage Area Characteristics

The project area is flat, with a slight slope from East to West that transitions North when it approaches the banks of Portage Creek. The area is also entirely wetlands with pockets of marshy areas and standing water. For design purposes, the areas that potentially affect the design have been divided into basins. This includes the new alignment for Portage Rd. since storm water will flow from the road onto the basins. However, the existing train tracks and proposed corridor are not included. This is because the proposed corridor has a 3.8% super elevation sloping from East to West. Additionally, it was assumed that the drainage from the existing train tracks is negligible due to infiltration. Furthermore, it was assumed culverts were placed underneath the existing tracks to allow drainage from the separated basins between the tracks. As the project design moves forward in the future, these assumptions will need to be analyzed more accurately to determine if they are applicable. For the purposes of this local review report, the assumptions made are valid.

The drainage basins used for Portage Creek and Placer River were provided by a study that HDR performed. Figures 1 and 2 as well as Tables 1 and 2 below show the characteristics that were used for the design considerations.

Table 1. Drainage Basin Characteristics

Drainage Basin Area (mi2) Precipitation (in) Portage Creek 56.73 183 Placer River 126.42 107

Seward Highway MP 75-90 – Portage Curve 2 Design Study Report

Figure 1. Portage Creek & Placer River Drainage Basins

Table 2. Storm Runoff Drainage Basins

Basin Perimeter (mi) Area (acre) A 0.39 5.7 B 0.49 7.3 C 0.89 19 D 0.56 13 E 0.62 2 ∑ Basins 2.90 47.0

Seward Highway MP 75-90 – Portage Curve 3 Design Study Report

Figure 2. A: Top Left; B: Top Right; C: Bottom Left; D: Bottom Right; E: Portage Rd.

Methodology

Section 7.1.9 of the Alaska Highway Drainage Manual states the approved hydrologic analysis methods. This includes using the specified 100-year FEMA flood insurance study, Log Pearson III, watershed regression equations, U.S. Army Corps of Engineers HEC-1 Flood Hydrograph, SCS and other unit hydrograph methods, and the rational method. Due to the limited amount of data provided, it was decided that the regression analysis and rational method would be used for bridge clearances and culvert design respectively. The procedure for these two methods was highly simplified for our local review. It is recommended that future studies be performed, as well as more than one method used for each design criteria. The Alaska Highway Drainage Manual also recommends that if possible, more than one method should be used to compare answers.

Design Criteria

Bridge Clearances – Regression Analysis

The project will have a bridge crossing over Portage Creek and Placer River. Per the Alaska Highway Drainage Manual, bridges require a 3-foot minimum above the governing waterline in the waterways it passes over. The reason for this is to protect the low chord of the bridges against debris and in particular for our region, ice, flowing underneath. As stated before, a 100-year flooding condition was used for the analysis of the basins that feed into Portage Creek and Placer River.

Seward Highway MP 75-90 – Portage Curve 4 Design Study Report

The Scientific Investigations Report 2016-5024 (Estimating Flood Magnitude and Frequency at Gaged and Ungaged Sites on Streams in Alaska and Conterminous Basins in Canada, Based on Data through Water Year 2012) from the United States Geological Survey (USGS) was used to determine the regression equation that applied to the project region (EQ. 1). To use this equation, two basin characteristics were needed, which was the drainage area and the average mean annual precipitation. These two characteristics were provided by HDR, and can be seen (Figure & Table 1) in the Drainage Area Characteristics. These regression equations have an inherent large percent error associated with each one. However, the Alaska Highway Drainage Manual insures that they are still an accurate representation of the flows that would be seen. Therefore, to be conservative, the upper limit flowrates were used for design purposes.

Once the peak flow rates were known, simple open channel flow calculations were performed to find the normal depth for the channel cross sections and associated flow rates. The channel cross sections were provided by HDR in a geotechnical report, and can be found below in Figures 3 & 4.

The cross sections were then modeled as trapezoidal and parabolic sections. This was done to provide an underestimation and overestimation to compare values with. The models and their equations (Sturm, 2009) are shown in Figure 5 below. As stated before, these rudimentary models were then used to calculate the water elevation in the channel for an associated flowrate.

To analyze the open channel flow, an elevation guess is made, which will ultimately provide a flowrate for the cross section using Manning’s Formula (EQ. 2) and the continuity equation (EQ.3). Then, using the goal seek function in Excel, the real elevation was found for the cross section by setting the calculated flow rate equal to the 1% chance exceedance flowrate calculated previously. Goal seek in excel then iterates through all the different elevation values until it finds an elevation that will provide a matching flow rate equal to the 1% chance exceedance flowrate. This method works because ultimately, all the variables involved end up being a function of the elevation. For the results of these methods, see Table 5 below.

Figure 3. Portage Creek Cross Section

Seward Highway MP 75-90 – Portage Curve 5 Design Study Report

Figure 4. Placer River Cross Section

Culvert Design- Rational Method

The project will have multiple sections where adequate drainage will be needed for the proposed corridor. Culverts will be placed to allow for this drainage where necessary. This will ensure the structural integrity of the subgrade of the road. The main consideration for the design of the culverts is storm water runoff. The culverts need to be able to carry enough precipitation during a storm event, as well as debris. Unique to the project’s region, the culverts also need to be designed to accommodate icing conditions. The limiting factor in culvert design is the flow rate. Therefore, picking a storm event, routing the data, and finally finding the flowrate is a necessity. Due to a limited amount of data, it was decided that the rational method would be used to find the flowrate.

Fortuitously, a rain gauge station from the National Oceanic and Atmospheric Administration (NOAA) is located on the project. This station is Portage 1 S (Site ID 50-7494). The annual maximum precipitation intensity data for the site was downloaded. From this data, an intensity-duration frequency relationship (IDF Curve) was developed. These curves can be found in Figure 5. Per the AHDM, culverts in designated flood areas are designed off the 100-year event. Therefore, the 100-year IDF curve was used in the following procedure. This can be seen in Figure 5 or EQ. 6.

In order to use the rational method (EQ. 4), the design storm average intensity, basin area, and rational coefficient need to be calculated. The basin areas were previously presented in Table 2 and Figure 2. To find the intensity, the time of concentration first needs to be found. In accordance with the AHDM, this was found using the equations presented in Appendix D. Using the equations presented there and the 100- Year IDF curve equation, the design intensity was found. To find the rational coefficient, a composite coefficient will need to be found using (EQ. 5). This is because the area is split up into 5 different basins that all have different characteristics. Figures 7 & 8 show the runoff coefficients used as well as their adjustment factors. These figures are a part of Appendix F from the Ohio Department of Transportation Hydraulics Manual (Ohio Department of Transportation, 2017). With the intensity, composite rational coefficient, and the total area, the demanded flow rate was then calculated.

Seward Highway MP 75-90 – Portage Curve 6 Design Study Report

Per the 9.2.2 in the AHDM, when icing conditions occur, the minimum size of culvert must be at least 36 inches in diameter. Therefore, 36 inches was chosen as the initial size check. Using Figure 6, the capacity of the culvert was determined using a similar technique to the open channel flow technique mentioned in the bridge clearance calculation. After the capacity of the culvert is found, it is then compared with the demand capacity. If the given is greater than the demand, then the culvert is okay to use.

The culvert was also checked for inlet and outlet control. This was done to ensure that erosion was mitigated at the entrance and exit for the culverts. This was done using the equations presented in 9.5.3 and 9.5.4 in the AHDM as well as Table 2 in Appendix A of the Culverts chapter.

Results

Bridge Clearances – Regression Analysis

It was found that the 100-Year Flood flows were 35,100 (cfs) and 41,800 (cfs) for the Portage Creek and Placer River waterways respectively. These results can be seen in Tables 3 & 4 below.

Table 3. Peak Flow Rates for Portage Creek Using Regression Analysis

Lower 95 Upper 95 Percent percent percent Average Percent chance chance -SEP , +SEP , prediction prediction P i P i SEP exceedance exceedance (percent) (percent) P,i interval flow, interval flow, (percent) flow, in ft3/s in ft3/s in ft3/s 50 5,700 1,980 16,400 -47.2 89.5 71.0 20 7,230 2,570 20,300 -46.6 87.1 69.3 10 8,310 2,950 23,400 -46.6 87.1 69.4 4 9,670 3,360 27,800 -47.2 89.6 71.1 2 10,700 3,630 31,300 -47.9 92.0 72.8 1 11,700 3,920 35,100 -48.6 94.4 74.5 0.5 12,800 4,130 39,600 -49.6 98.3 77.3 0.2 14,200 4,350 46,200 -51.1 104.6 81.8

Table 4. Peak Flow Rates for Placer River Using Regression Analysis

Lower 95 Upper 95 Percent percent percent Average Percent chance chance -SEP , +SEP , prediction prediction P i P i SEP exceedance exceedance (percent) (percent) P,i interval flow, interval flow, (percent) flow, in ft3/s in ft3/s in ft3/s 50 6,430 2,250 18,400 -47.1 89.2 70.8 20 8,370 2,980 23,500 -46.5 86.8 69.1 10 9,720 3,460 27,200 -46.5 86.8 69.1 4 11,400 3,990 32,700 -47.2 89.2 70.9 2 12,700 4,330 37,100 -47.8 91.6 72.6 1 14,000 4,690 41,800 -48.5 94.0 74.3 0.5 15,300 4,960 47,200 -49.5 97.9 77.1 0.2 17,000 5,250 55,300 -51.0 104.1 81.5

Given the results in Table 5 as well as the channel cross sections in Figures 3 & 4, it was determined that the flood lines were 19 feet and 29 feet for Placer River and Portage Creek respectively. This value is the

Seward Highway MP 75-90 – Portage Curve 7 Design Study Report

elevation above sea level, and uses the maximum calculated elevation for each cross section. Therefore, the lowest chord of the bridges must be at least 3 feet above these elevations.

Table 5. Peak Flow Elevations

Trapazoidal Model Placer River Portage Creek

n S Kn Q nSKn Q (ft/ft) (cfs) (ft/ft) (cfs) 0.04 0.02 1.486 41800 0.058 0.02 1.486 31500 y (guess) b h m B y (guess) b h m B (ft) (ft) (ft) (ft/ft) (ft) (ft) (ft) (ft) (ft/ft) (ft) 6.700508 315.5 14 7.142857 411.2215 10.39272 125 13 9.615385 324.8600764

A P R v Q Q error A P R v Q Q error (ft2) (ft) (ft) (ft/s) (cfs) (cfs) (ft2) (ft) (ft) (ft/s) (cfs) (cfs) 2434.702 412.1551 5.907247 17.16843 41800 -0.00048 2337.636 325.938 7.172026 13.47515 31500.00002 -2.4E-05

Parabolic Model Placer River Portage Creek

n S Kn Q nSKn Q (ft/ft) (cfs) (ft/ft) (cfs) 0.04 0.02 1.486 41800 0.058 0.02 1.486 35100

y (guess) B1 y1 B x y (guess) B1 y1 B x (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) (ft) 10.0208 438 17 336.2798 0.119196 14.7549 203 13 216.2681 0.272900162

A P R v Q Q error A P R v Q Q error (ft2) (ft) (ft) (ft/s) (cfs) (cfs) (ft2) (ft) (ft) (ft/s) (cfs) (cfs) 2246.528 337.0744 6.664783 18.60649 41800 -2.3E-08 2127.343 218.9233 9.717299 16.49945 35100.00006 -6.4E-05

Culvert Design – Rational Method

Using the rational method described previously, it was found that the 100-Year storm flow rate was 6.3 cfs. Additionally, with an assumed slope of 2%, it was found that a 36-inch culvert has a capacity of 46.52 cfs. In conclusion, the 36-inch culvert should be plenty adequate to hold the demanded flow while also providing enough room for debris and icing conditions. It was also found that the normal depth in the culvert during the 100-year storm event is 0.2 feet and the critical depth is 0.45 feet. Since the critical depth is higher than the normal depth, that means that the flow will be super-critical during the governing condition. Additionally, the slope of the culvert is classified as steep, which might require inlet control. Therefore, it is recommended that either rip rap, a vegetative barrier, a pan, or some sort of retardant be placed to slow the flow of water at the entrance to mitigate erosion effects. When the outlet control was being analyzed, it was assumed that the culvert was in the flowing full condition. This means it was flowing at its max capacity. After finding the height of the tail water at the exit based on the barrel losses, it was determined that the tail water height was 1.67 feet and having an exit velocity of 9.5 feet per second. This is conducive to flow type III, where the tail water height is larger than the critical depth. The exit velocity was determined to be a bit high. Therefore, it was recommended that the same precautions as the inlet control be taken for outlet control to mitigate erosion. All of the calculations performed in this section can be seen in Tables 6, 7, & 8.

Seward Highway MP 75-90 – Portage Curve 8 Design Study Report

Figure 5. Flow Type Classification (AHDM Chapter 9)

Intensity-Duration-Frequency Relationships for Portage, Alaska NOAA Station: Portage 1 S (Site ID: 50-7494) 1.2

1 y = 0.3608x-0.419 2-Year IDF Curve y = 0.5177x-0.442 0.8 y = 0.6232x-0.445 5-Year IDF Curve y = 0.7561x-0.439 10-Year IDF Curve y = 0.8686x-0.447 0.6 y = 0.9557x-0.437 25-Year IDF Curve y = 1.093x-0.439 50-Year IDF Curve y = 1.2848x-0.446 Intensity (in/hr) Intensity 0.4 y = 1.4319x-0.449 100-Year IDF Curve 200-Year IDF Curve 0.2 500-Year IDF Curve 1000-Year IDF Curve 0 0 200 400 600 800 1000 1200 1400 1600 Duration (hr)

Figure 6. IDF Curves

Seward Highway MP 75-90 – Portage Curve 9 Design Study Report

Table 6. Determination of Peak 100-Year Storm Flow

Sheet Flow From Portage Rd. Determination Of Adjusted Composite Runoff Coefficient

L n P2 s Tt

(ft) (in) (ft/ft) (hr) AA AB AC AD AE AT 15 0.011 2.28649 0.02 0.005237 (acre) (acre) (acre) (acre) (acre) (acre) 5.7 7.3 19.0 13.0 2.0 47.0

Shallow Concentrated Flow From Basins

CA CB CC CD CE Cf s V 0.2 0.2 0.2 0.2 0.9 1.25 (ft/ft) (ft/s) 0.001 0.510218

CT

LA LB LC LD 0.287234 (ft) (ft) (ft) (ft) 711 907 1787 1030 Peak 100-Year Storm Flow

TA TB TC TD Tt

(hr) (hr) (hr) (hr) (hr) I C A FP Q 0.38709 0.493798 0.972896 0.560763 2.414547 (in/hr) (acre) (cfs) 0.649548 0.287234 47 0.72 6.313606

Total Concentration Time

TT (hr) 2.419784

Table 7. 36" CSP Design Check & Flow Classification

Culvert Demand From 100-Year Storm Design Check Q 6.313606 cfs PASS

Capacity Of 36" Culvert (Flowing Full) Slope & Flow Clasification

S0 0.02 ft/ft Steep Slope n 0.02 Super-Critical Flow

kn 1.486 Inlet Controlled g 32.2 ft/s2 Install Pan Or Rip-Rap d 3.00 ft y 3.00 ft 1-2(y/d) -1 θ 360 ° 6.28 rads A 5.99 ft2 P 9.42 ft R 0.64 ft Q 46.52 cfs

Find Normal Depth For Demand Find Critical Depth For 36" CSP d 3.00 ft d 3.00 ft

y 0.20 ft yc 0.45 ft 1-2(y/d) 0.868495 1-2(y/d) 0.701575 θ 59.43157 ° θ 90.89295 ° 1.04 rads 1.59 rads A 0.88 ft2 A 1.55 ft2 P 1.56 ft B 2.982965 ft R 0.57 ft D 0.52 ft Q 6.31 cfs v 4.08 ft/s Q Error 0.00 cfs F 1.00

Seward Highway MP 75-90 – Portage Curve 10 Design Study Report

Table 8. Determination of Head Loss & Tail Water Effects

Velocity Head Entrance Loss Exit Loss

Hv KE HE Ho (ft) (ft) (ft) 0.936793061 0.5 0.468397 0.936793

Friction Loss

n L R P Hf (ft) (ft) (ft) (ft) 0.02 100 0.64 9.42 1.985745

Barrel Losses Find Loss In Specific Energy H y E ΔE (ft) (ft) (ft) (ft) 3.390934921 1.9996 5.94 2.545458

Find Tail Water Depth Q 46.52 cfs

S0 0.02 ft/ft n 0.02

kn 1.486 g 32.2 ft/s2 d 3.00 ft y (guess) 1.67 ft 1-2(y/d) -0.11333 θ 193.015 ° Find Associated Tail Velocity 3.37 rads v A 4.89 ft2 (ft/s) E 3.07 ft 9.506406575 E Error 0.53 ft

Limitations

Bridge Clearances – Regression Analysis

The methods used were very one dimensional and rudimentary. Using Manning’s Formula implies that gradually varied flow is assumed to be negligible. Also, other effects such as backwater, hydraulic jumps, and tidal effects were not explored in this local review. In the future, it is recommended that a more in depth model be developed in HEC-RAS, or another similar software. Additionally, more effects on the peak flow must be taken into consideration.

Culvert Design

Different techniques should be used to generate more peak flow rate values. A broader value is best for comparison, and using just one technique is risky when it comes to design. Also, when calculating concentration time, it was assumed culverts run underneath the train tracks in order to connect the drainage basins. Even if this is true, the time it takes for the water to travel through the culverts was not included. Other effects such as stage, storage, and infiltration were not included, and may need to be considered in the future. Additionally, basins were drawn in Google Earth and chosen from judgement. This technique carries an inherent percent error with it.

Seward Highway MP 75-90 – Portage Curve 11 Design Study Report

Recommendations

The following is a summary of the recommendations from this report:  With respect to a 100-year flood, flood lines for Portage Creek and Placer River bridges are 29 feet and 19 feet above sea level, respectively  Lowest bridge chord must be at least 3 feet above aforementioned flood lines  36 inch culverts will be adequate in the project area with respect to a 100-year storm

Equations

Figure 7. Channel Cross Section Properties, from Open Channel Hydraulics (Strum)

Seward Highway MP 75-90 – Portage Curve 12 Design Study Report

11.4 ∗ . ∗ . (EQ. 1)

Where: ;

∗ ∗ (EQ. 2)

Where: 1.486 ; ; ; ; ; ⁄

∗ (EQ. 3)

∗ ∗ (EQ. 4)

Where: ∗ ⁄ ∗ ∗ sec; ⁄ ;

∑ ∗ (EQ. 5) ∑

0.9557 ∗ . (EQ. 6)

Works Cited

Alaska Department of Transportation and Public Facilities. (2006, June 15). Alaska Highway Drainage Manual. Highway Drainage Manual. Juneau, Alaska, United States of America. Curran, J. H., Barth, N. A., Veilleux, A. G., & Ourso, R. T. (2016). Estimating Flood Magnitude and Frequency at Gaged and Ungaged Sites on Streams in Alaska and Conterminous Basins in Canada, Based on Data through Water Year 2012. Reston, Virginia: U.S. Geological Survey Science Publishing Network, Tacoma Publishing Service Center. Ohio Department of Transportation. (2017). Hydraulics Manual. Columbus. Sturm, T. W. (2009). Open Channel Hydraulics. New York City: Mcgraw-Hill Education.

Seward Highway MP 75-90 – Portage Curve 13 Design Study Report

Miscellaneous Design Criteria

Figure 8. Appendix A, Chapter 7 of AHDM

Figure 9. Appendix A, Chapter 9 of AHDM

Seward Highway MP 75-90 – Portage Curve 14 Design Study Report

Figure 10. Appendix D, Chapter 7 of AHDM

Figure 11. Appendix D, Chapter 7 of AHDM

Seward Highway MP 75-90 – Portage Curve 15 Design Study Report

Figure 12. Head Loss Formulas from Chapter 9 of AHDM

Seward Highway MP 75-90 – Portage Curve 16 Design Study Report

Figure 13. Table 2 In Appendix A of Chapter 9 of AHDM

Seward Highway MP 75-90 – Portage Curve 17 Design Study Report

Figure 14. Runoff Coefficients for Rational Method Provided by ODOT Hydraulic Manual

Figure 15. Runoff Coefficient Adjustment Factors from ODOT Hydraulic Manual

Seward Highway MP 75-90 – Portage Curve 18 Design Study Report

Seward Highway MP 75-90 – Portage Curve Design Study Report

APPENDIX F

Bridge Preliminary Design

Seward Highway MP 75-90 – Portage Curve Design Study Report

Preliminary Bridge Design Report

Seward Highway Milepost 75-90 Rehabilitation Project Portage Curve Project No.: OA3/58105

Group D

Prepared For: State of Alaska Department of Transportation and Public Facilities 4111 Aviation Avenue Anchorage, Alaska 99519

Prepared By: Seawolf Engineering 2900 Spirit Drive, Room 205 Anchorage, AK 99508

Author:

Kyle Powell

Seward Highway MP 75-90 – Portage Curve Design Study Report

Table of Contents

1.0 Introduction……………….……………………...……………………………………………………1 2.0 Design Criteria……………….……………………...…………………….……………………………1 2.1 Alternatives……………….……………….…...……………………………………………………1 2.2 Super Elevation……………….……………………...... …………………………………………1 2.3 Radius for Horizontal Curve……………….………….……………….……………………………1 2.4 Clearance……………….……………………...………………………….…………………………1 2.5 Site Conditions……………….……………………...………………………………………………2 2.6 Girders……………….……………………...…………………………….…………………………2 2.7 Design Loads…………………………………...……………………………………………………2 3.0 Substructure……………….……………………...………………………….…………………………2 3.1 Piers……………….……………………...…………………………………………………………3 3.2 Abutments.……………………...……………………………………………………………………3 4.0 Cost Estimate.……………………...……………………………...……………………………………3 5.0 Plan Set and Typical Sections.……………………...…………………………………..………………6

Seward Highway MP 75-90 – Portage Curve Design Study Report

1.0 Introduction

The realignment of the horizontal curve between MP 78 and 79 means both existing bridges at Placer River and Portage Creek No. 1 will need to be replaced. New bridges will be constructed at new locations which is determined from the preferred alignment option. The following sections detail the design and consideration for the structure’s crossing Portage Creek No. 1, and Placer River, on the Seward Highway. These bridges and their associated design will assist in creating a safer roadway for drivers.

2.0 Design Criteria

2.1 Alternatives

Multiple alternative design options for each bridge were analyzed on the basis of cost and constructability. Varying the number of spans for each bridge resulted in minimal changes to the total cost of the bridge. As such, it was determined that constructability would be the deciding factor for choosing an alternative. Since construction of each bridge will require piles and piers to be driven and constructed in a river, the least number of spans necessary was the final decision for each bridge. The final, individual span lengths for each bridge will be set at 145 feet.

2.2 Super Elevation

The super elevation criteria for both bridges was determined in the initial planning of the project in order to create a safer roadway for users. The roadway will be built on a 3.8% super elevation for the length of the project which means both bridges will be built with that super elevation along the entire span. The super was accounted for in the general layout for both the piers, and the abutments that support the structure. Each pier and abutment will have a bearing surface set at a 3.8% slope and support the girders at the associated angles.

2.3 Radius from Horizontal Curve

The preferred alignment has a radius of curvature set at 2150 feet. Each bridge was designed to support the roadway despite the precast concrete girders being chorded. The chord offset was checked for each bridge to determine if a cast-in-place concrete deck would be required to accommodate the radius of curvature. The following equation was used to determine the chord offset:

∗ /

where: R = Radius of Horizontal Curve (ft) and d = span length * 360 / (2 * pi *R)

If the determined chord offset is greater than one then a cast-in-place concrete deck will be required for the bridge. Using a span length of 145 feet and a radius of 2150 feet, a chord offset length of 1.22 feet is computed. Therefore, both bridges will need a cast-in-place concrete deck constructed before either one can be paved.

2.4 Clearance

A primary consideration of the substructure design was maintaining sufficient clearance of both Portage River No.1 and Placer River. A 100-year flood analysis was performed for each river to determine the elevation of maximum flow. An additional three feet of clearance is required to allow

Seward Highway MP 75-90 – Portage Curve 1 Design Study Report

for safe passage of ice drifts and other potential hazards to the structure. The required clearances for each bridge are as follows:

Placer River Bridge: 22 feet (Measured from zero sea-level) Portage Creek No. 1 Bridge: 29feet (Measured from zero sea-level)

The calculations for these elevations are discussed in more detail in Appendix E.

2.5 Site Condition

Site conditions were a consideration for the substructure design. The controlling condition for pier, and abutment design is the liquification prone soils in the area. Due to the high hazard of earthquakes in the area, piles are to be driven a minimum of 120 feet, and require minimum diameter of 24” for the abutments, and 48” for the piers. These considerations will sufficiently increase project costs.

2.6 Girders

A bulb-tee girder with a height of 5.5 feet was chosen for both bridges. The 5.5-foot girder was chosen over the shorter 3.5 and 4.5-foot girders mainly due to the span length it can achieve. The 5.5- foot girder can span up to 145 feet which would be sufficient for any required span for the project. The longer span will reduce the number of piers required to span Placer River. Additionally, the deeper 5.5-foot girders have a larger capacity which means that less girders are required to resist all the forces that will act on the bridge.

Another alternative associated with the girders that was explored was forming the girders with the radius of the roadway. This alternative would allow for cleaner connections at piers but was determined to no be cost effective for the larger radius of the bridge. The proposed design used straight girders that will be offset at each pier to account for the radius. A cast in place concrete deck will be needed for the chosen design.

2.7 Design Loads

Design loads were not a significant concern for this level of design. Using the AKDOT’s “Alaska Bridges and Structures Manual” a girder was chosen that is commonly used for similar roadways. The AKDOT has supporting calculations in the manual that show each girder can support half a lane of roadway. Therefore, the bridges were design in a minimum of girders per lane of roadway, but the controlling factor for number of girders was the width of the structure.

3.0 Substructure

The substructure considered for both bridges considered includes selection of a steel pile, and the length driven for the piles. Substructure design was based on criteria detailed in the “Alaska Bridges and Structures Manual.” Concrete cast in place around the piers and abutment was not considered in this design.

3.1 Piers

The Alaska Bridges and Structures Manual specifies that a 48-inch diameter steel pile with 1 inch thick walls should be used for a pier that exceeds 15 feet in height. The number of piles per pier was

Seward Highway MP 75-90 – Portage Curve 2 Design Study Report

calculated by subtracting the number of girders used for the bridge by two. Per the Alaska Bridges and Structures Manual each 48-inch pile will be filled 55 feet down with CIP concrete.

3.2 Abutments

The “Alaska Bridges and Structures Manual,” section 8-6, specifies 24” diameter with 1/2” thick walls steel piles be used for abutments in regions with liquefiable soils. The number of piles per abutment is based on one pile “per girder reaction.” Per the Alaska Bridges and Structures Manual each 24” pile will be filled 55 feet down with CIP concrete.

4.0 Cost Estimate

Section 8-6 of the Alaska Bridges and Structures Manual specifies cost codes, items, rounding accuracy, and unit cost of each pay item. Relevant pay items were chosen and can be seen in Table 1 and 2 below. Unit costs were estimated based on values given in the bridge manual and recent DOT estimates provided.

The preliminary cost estimate can be found in Table 1 and 2 below. The cost estimate includes 10% for mobilization and 15% for construction. Since this is a preliminary design, a 15% contingency was added to the cost estimate for each bridge to account for any future changes to the design. As more information on the design comes available, the contingency value will be reduced accordingly.

Seward Highway MP 75-90 – Portage Curve 3 Design Study Report

Item Unit No. Pay Item Unit Price Quantity Amount Removal of Existing 202(14) Bridge SF $40 16458 $658,320 205(6) Structural Fill CY $35 $0 501(1) Class A Concrete CY $1,750 819 $1,433,250 501(2) Class A-A Concrete CY $1,500 320 $480,000 Precast Concrete 501(7) Member lbs $0.50 5800704 $2,900,352 503(1) Reinforcing Steel lbs $2.00 196819 $393,638 Epoxy-Coated 503(2) Reinforcing Steel lbs $2.25 98409.6 $221,422 Furnish Structural Steel 505(5) Piles (24"x1/2") LF $150 1920 $288,000 Furnish Structural Steel 505(5) Piles (48"x1") LF $500 3600 $1,800,000 Drive Structural Steel 505(6) Piles (24"x1/2") EA $10,000 16 $160,000 Drive Structural Steel 505(6) Piles (48"x1") EA $35,000 24 $840,000 507(1) Steel Bridge Railing LF $225 1300 $292,500 Waterproofing 508(1) Membrane SY $25 2889 $72,222 606(16) Transition Rail EA $3,000 4 $12,000 611(1) Riprap, Class II CY $75 $0 Geotextile, Erosion 631(2) Control, Class 1 SY $3.00 $0 Mobilization and 640(1) Demobilization % 10% $955,170.42

Contingency % 15% $1,576,031,20 Construction Engineering % 15% $1,812,435.88 Total ~$13,895,000 Table 1. Placer River Bridge Cost Estimate

Seward Highway MP 75-90 – Portage Curve 4 Design Study Report

Item Unit No. Pay Item Unit Price Quantity Amount Removal of Existing 202(14) Bridge SF $40 6867 $274,680 205(6) Structural Fill CY $35 $0 501(1) Class A Concrete CY $1,750 550 $962,500 501(2) Class A-A Concrete CY $1,500 138 $207,000 Precast Concrete 501(7) Member lbs $0.50 2454144 $1,227,072 503(1) Reinforcing Steel lbs $2.00 118886 $237,773 Epoxy-Coated 503(2) Reinforcing Steel lbs $2.25 59443.2 $133,747 Furnish Structural Steel 505(5) Piles (24"x1/2") LF $150 2640 $396,000 Furnish Structural Steel 505(5) Piles (48"x1") LF $500 2400 $1,200,000 Drive Structural Steel 505(6) Piles (24"x1/2") EA $10,000 22 $220,000 Drive Structural Steel 505(6) Piles (48"x1") EA $35,000 16 $560,000 507(1) Steel Bridge Railing LF $225 600 $135,000 Waterproofing 508(1) Membrane SY $25 1867 $46,667 606(16) Transition Rail EA $3,000 4 $12,000 611(1) Riprap, Class II CY $75 $0 Geotextile, Erosion 631(2) Control, Class 1 SY $3.00 $0 Mobilization and 640(1) Demobilization % 10% $561,243.87 Construction Engineering % 20% $1,122,487.73 Total ~$7,300,000 Table 2. Portage Creek #1 Bridge Cost Estimate

Seward Highway MP 75-90 – Portage Curve 5 Design Study Report

5.0 Site Plan and Typical Sections

Figure 1. Placer River Bridge Plan Set

Seward Highway MP 75-90 – Portage Curve 6 Design Study Report

Figure 2. Portage Creek No. 1 Plan Set

Seward Highway MP 75-90 – Portage Curve 7 Design Study Report