Travel Demand Forecasting
The Lane Council of Governments (LCOG), the MPO for the Eugene-Springfield area in Oregon, uses CTPP data in travel demand forecasting. For example, LCOG has found CTPP data to be essential in developing models for smaller communities in Lane County. Many of these communities have no household travel surveys, so the CTPP is one of the few sources of local travel data. CTPP data allow LCOG to calibrate the trip distribution model for work trips in these small communities. To do this, LCOG forecasters use the flow data from the CTPP with data from the trip generation model, based upon current land use, in an iterative proportional fitting procedure that scales the flows into a trip table.
Travel Demand Forecasting
Forecasters at the Metropolitan Transportation Commission (MTC), the MPO for the San Francisco Bay area, use the journey to work data in CTPP for calibrating and validating their work trip distribution model. The journey to work data serve as observed work trip data in the calibration and validation process.
MTC forecasters convert CTPP data to a form that can be used in the model. Because the CTPP gives information on workers, a conversion factor must be applied to convert the CTPP data from workers to trips. Once this conversion is made, the CTPP data are ready to be used to validate the home-based work trip distribution model. For example, the CTPP data can provide the observed trip length frequency distribution for comparison with the model estimated frequency distribution.
Trend Analysis
The CTPP provides a rich source of data for analyzing trends in local areas. Consistent methods and consistent questions over time allow for comparisons between 1980, 1990 and 2000. The consistency of the CTPP was a key factor when the Chicago Area Transportation Study (CATS) studied downtown commuting patterns.
CATS used 1980 and 1990 CTPP data to examine the county of origin and means of transportation for downtown Chicago workers. The CTPP showed that the majority of work trips to downtown were made by transit, but that transit's share declined from 1980 to 1990. CTPP data also allowed CATS to examine geographic shifts in employment within the downtown area.
CTPP 2000 will enrich these types of trend analyses by providing data at another time point, thus enabling transportation planners to understand how travel patterns have changed over time in their communities.
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"AASHTO and its members are pleased to work with the U.S. Department of Transportation and the Census Bureau to provide CTPP 2000 to the states and Metropolitan Planning Organizations (MPOs) in a faster and easier way. This Census data is a critical part of the information needed for states and MPOs to carry out their transportation planning mission."
John Horsley
American Association of State Highway and Transportation Officials (AASHTO),
Executive Director
Examples of flow maps showing trips over the Golden Gate Bridge and the Oakland Bay Bridge from travel demand models.
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