What is modeling?
Many of the transportation planning activities performed by SRTC require Travel Demand Modeling. Modeling is a method of forecasting how society will use the transportation system now and 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 individual decisions on how, where and when to travel.
Modeling analysis explores various modes of travel including walking, biking, bus, auto and carpool. Modeling considers the demand on the transportation system and assists the public, community leaders, and partner agencies in making transportation decisions and investments.
The model contains inventories of existing roadway and transit facilities and of all housing and employment in the area. Using the model, transportation planners can estimate future traffic and transit volumes without the costs of building inappropriate roadways or waiting for traffic congestion to severely impact travelers.
SRTC is federally certified to conduct regional transportation modeling, and provides transportation modeling services to public jurisdictions and agencies in Spokane County. In house, models are used extensively for developing the Metropolitan Transportation Plan (MTP), a 20 year ‘blueprint’ for transportation planning SRTC is required to update every four years.
Transportation Modeling Programs used by SRTC
SRTC does several kinds of modeling, using different software, including:
Travel demand model – VISUM software
- Used to predict transportation measures such as traffic volumes, transit ridership and congestion 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, and building permits.
- Travel demand results are often the input for intersection and air quality models.
VISUM is implemented in Spokane as a traditional “4-step” model:
- Trip Generation (land-use & economic factors determine how many trips people will make)
- Trip Distribution (determines where trips start and end)
- Mode-choice (determination of how you get to your destination; e.g., bus, walk, auto, etc.)
- Trip Assignment (determination of which path you take from your trip origin to your trip destination)
Air quality modeling – CAL3QHC and MOVES
Spokane is designated as an attainment area for Carbon Monoxide (CO) and PM10,, operating under maintenance plans since August of 2005 (for more information on Air Quality, see the Air Quality page of this website). On-road mobile sources such as vehicles produce an estimated 67% of the total CO emissions for the Spokane area. As a result, SRTC is charged with Air Quality modeling to ensure that future transportation choices will not impact our air quality in a negative way.
CAL3QHC is a modeling program that predicts air quality impacts of carbon monoxide (CO), nitrogen dioxide (NO2), particulate matter (PM), and other inert pollutant concentrations from moving and idling motor vehicles at or alongside roadways and roadway intersections.
It is used for ‘Hot-Spot Analysis;’ determining the air quality levels in specific locations. Inputs used with this program include emission factors, roadway geometries, signal timing, weather conditions, site-specific conditions, current traffic volumes, and forecast traffic volumes.
MOVES (MOtor Vehicle Emission Simulator) is a modeling system that estimates emissions for mobile sources covering a broad range of pollutants. MOVES currently estimates emissions from cars, trucks & motorcycles.
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:
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.
Documentation for the latest updates to the regional travel demand model is available here:
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 networks, operating characteristics, households and employment by traffic 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 and email it to email@example.com.