Travel Demand Model

Many of the transportation planning activities performed by SRTC require Travel Demand Modeling; a method of representing how

Screenshot from SRTC’s Travel Demand Model

people use the transportation system now and forecasting travel behavior in the future. Modeling involves the use of computer software to represent how travel choices are made. Travel demand occurs as a result of thousands of individual travelers making decisions on how, why, where, and when to travel.

Modeling analyzes modes of travel including walking, biking, bus, personal vehicles and carpool. Modeling takes into consideration the demand on the transportation system and assists community leaders and partner agencies in making transportation investment decisions.

SRTC’s travel demand model contains inventories of existing transportation facilities and of all housing, shopping and employment in the area. Using the model, transportation planners can estimate future traffic volumes and transit ridership. This helps agencies plan for appropriate scale facilities and services.

SRTC is required to conduct regional transportation modeling and provides transportation modeling services to public jurisdictions and agencies in Spokane County. The model is used extensively for developing the Metropolitan Transportation Plan (MTP), a 20+ year ‘blueprint’ for transportation planning, which SRTC is required to update every four years.

SRTC currently uses the VISUM software for regional travel demand modeling. The model is used to evaluate transportation measures such as transit ridership, traffic volumes, miles traveled, travel speeds, and delay on the regional transportation system. The model’s land use data comes from a variety of sources: WA State Employment Security Department, Department of Revenue, Department of Health, Census, comprehensive plans, and building permits. Results from the travel demand model are often used for corridor studies, subarea plans, and air quality analysis.

SRTC uses a “4-step” model:

  1. Trip Generation (land-use & economic factors determine how many trips people will make)
  2. Trip Distribution (determines where trips start and end)
  3. Mode-choice (determination of how you get to your destination; e.g., bus, walk, drive, etc.)
  4. Trip Assignment (determination of which path you take from your trip origin to your trip destination)

Travel Forecasting Documentation
Federal transportation planning regulations require documentation of the input assumptions and methods used for developing travel forecasts [23 CFR 450.316]. The documentation of the 2013 MTP Update, Horizon 2040, includes an inventory of the current state of transportation in the planning area, key planning assumptions used in developing forecasts, and descriptions of the methods used to develop forecasts of future travel demand. The documentation and corresponding appendices are located here:

Land Use Documentation and Planning Assumptions

In November 2015, SRTC hosted a model peer review meeting to receive feedback from national experts on the Spokane regional model compared to the state of the travel demand modeling practice. The primary objective of the peer review was for SRTC to better understand the capabilities of the current model and help SRTC decide how to proceed with model improvements. The peer review was sponsored and supported by the Federal Highway Administration’s Travel Model Improvement Program (TMIP). An overview of the peer review and the resulting recommendations are summarized in the SRTC Model Peer Review Report.

Model Data
As a service to SRTC partner agencies and the consulting firms they work with, SRTC provides transportation modeling data in an effort to ensure regionally consistent transportation studies in Spokane County. That data can include transportation networks, operating characteristics, households and employment by transportation analysis zones, and modeling assumptions. This information is provided free of charge, although there may be minimal costs associated in reproducing this information.

In order to receive transportation modeling data, please fill out this Model Data Request Form updated and email it to contact.srtc@srtc.org.