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Major Transportation Corridor Studies Using an EMME/2 Travel Demand Forecasting Model: The Trans-Lake Washington Study. Carlos Espindola, Youssef Dehghani and Cathy Strombom Parsons Brinckerhoff, Inc. October 18-20, 2000

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Major Transportation Corridor Studies Using an EMME/2 Travel Demand Forecasting Model: The Trans-Lake Washington Study

Carlos Espindola, Youssef Dehghani

and Cathy Strombom

Parsons Brinckerhoff, Inc.

October 18-20, 2000

15th Annual International EMME/2 Users’ Group Conference, Vancouver, BC.


Outline l.jpg
Outline Demand Forecasting Model: The Trans-Lake Washington Study

  • The Project

  • The Alternatives

  • Mini Validation

  • Coding Challenges

  • Problems Encountered

  • Measures of Effectiveness

  • Looking Ahead

  • Acknowledgements


The project l.jpg
The Project Demand Forecasting Model: The Trans-Lake Washington Study

  • Identify “reasonable and feasible solutions” to improve mobility across/or around Lake Washington

  • Three facilities were studied: SR-520, I-90 and SR-522

  • Projected regional growth: 50% more person trips over the next 25 years

  • Using EMME/2 based four- step model (Puget Sound Regional Council)


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Study Demand Forecasting Model: The Trans-Lake Washington StudyArea


The alternatives l.jpg
The Alternatives Demand Forecasting Model: The Trans-Lake Washington Study

  • 6 alternatives plus No-Build

  • No-Build

    • SR-522: 2 GP lanes in each direction

    • SR-520: 2 GP lanes in each direction

    • I-90: 3 GP lanes plus 2 reversible center lanes

  • Metropolitan Transportation Plan (MTP, 1998)

    • bus-only lanes on SR-522

    • HOV lanes on SR-520

    • LRT on I-90 center lanes

    • some TDM improvements


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The Alternatives (cont.) Demand Forecasting Model: The Trans-Lake Washington Study

  • MTP “Flipped”

    • new LRT bridge along SR-520

    • continuous 2-way HOV lanes on I-90 center lanes

  • Roadway/Rail

    • new LRT bridge along SR-520

    • LRT on I-90 center lanes


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The Alternatives (cont.) Demand Forecasting Model: The Trans-Lake Washington Study

  • New Crossings

    • a new four-lane arterial connection across the lake north of SR-520 and HOV lanes on SR-520

    • LRT on new arterial bridge and on I-90

  • Roadway/Bus

    • new four-lane freeway with HOV lanes

    • improved bus service & passenger only ferry

    • 2-way 24 hour HOV lanes on I-90 center lanes


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The Alternatives (cont.) Demand Forecasting Model: The Trans-Lake Washington Study

  • Maximize Alternatives

    • passenger-only ferry

    • conversion of one GP lane to HOV lane on SR-520

    • LRT on I-90 center lanes

    • very aggressive TDM package including congestion-pricing measures


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Mini Validation Demand Forecasting Model: The Trans-Lake Washington Study

  • Screenline comparison of vehicle volumes: observed vs. modeled

  • Tolerance: + 10%

  • Highway Assignment

    • Data: AWDT

    • Daily variation of traffic volumes

  • Transit Assignment

    • Data: observed and Sound Transit (ST) model


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Coding Challenges Demand Forecasting Model: The Trans-Lake Washington Study

  • Transportation demand management

    • Equivalent parking cost

  • Congestion Pricing

    • Time equivalency of toll


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Problems Encountered Demand Forecasting Model: The Trans-Lake Washington Study

  • The “flip-flop” effect

    • What? Large variation in number of trips across the lake (validation)

    • Why? Caused by congestion (constrained capacity) in Trans-Lake facilities

    • How? Trip distribution (gravity model) reduces trips across the lake – search for equilibrium between supply and demand

    • Then? Consistency in application from one alternative to another


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Congestion Pricing Demand Forecasting Model: The Trans-Lake Washington Study

  • Feasibility of tolls on cross lake trips (demand management)

  • Cross lake demand got depressed (“lost” over 100,000 daily trips)

    • caused unrealistic demand estimates for transit and HOVs

  • What to do?

    • Introduce toll on assignment only

    • Or two step process


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Congestion Pricing (cont.) Demand Forecasting Model: The Trans-Lake Washington Study

  • Two step process

    • Suppressed demand for non-HOVs

      • Model run with toll, lane conversion and parking costs

    • Un-suppressed demand for HOVs and transit

      • Model run without toll, lane conversion or parking costs

    • Highway and transit assignments


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Measures of Effectiveness Demand Forecasting Model: The Trans-Lake Washington Study

  • To help evaluate and compare the performance of the alternatives

    • Vehicle trips by facility and mode (NCPL, HOV and Commercial vehicles)

    • Person trips by facility and mode (same as above plus Transit), screenline mode shares were produced

    • Weighted average PM peak period travel time in minutes between designated districts


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Measures of Effectiveness (cont.) Demand Forecasting Model: The Trans-Lake Washington Study

  • From select link analysis on each facility:

    • PM peak period vehicle miles of travel (VMT)

    • PM peak period vehicle hours of travel (VHT)

    • PM peak period speeds

    • weighted average trip lengths both in distance and time

  • Peak period and hourly vehicular traffic, capacity and v/c ratio by facility and direction

  • Peak period person through-put by facility, mode and direction


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Looking Ahead Demand Forecasting Model: The Trans-Lake Washington Study

  • Use of Composite Impedance in trip distribution to reflect both highway and transit improvements

  • Update base year (1998)

  • Define the use of “new” vs. current version of PSRC model

  • Look at better way to forecast 3+ HOVs


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Summary Demand Forecasting Model: The Trans-Lake Washington Study

  • A tool to identify “reasonable and feasible solutions” to improve mobility across/or around Lake Washington

  • Helps evaluate a wide variety of transportation improvements (focus on mode, location and amount of change)


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Acknowledgements Demand Forecasting Model: The Trans-Lake Washington Study

  • Washington State Department of Transportation – Office of Urban Mobility (WSDOT/OUM)

  • Puget Sound Regional Council (PSRC)

  • Trans-Lake Washington Consulting Team