Methodologies For Assessing The Impacts Of Highway Capacity Enhancements On Travel Behavior

Acceptance of ITS components that are designed to increase capacity will hinge on the extent to which additional capacity induces additional travel. This study addressed methodologies for studying the effects of capacity on travel: 1) before and after studies or travel times and volumes in corridors in which capacity had been increased, 2) surveys of users of routes on which capacity had been increased, and 3) statistical changes in county VMT as a function of freeway capacity. On I-80 in the Bay Area, the site selected for the investigation, travel times and volumes were quite variable. This suggests that a fairly high volume of data are required to draw conclusions about changes in volumes. Furthermore, construction destroyed most of the existing loop detectors, and new detectors were not connected immediately. Thus such comparisons may not be possible in the short term if researchers do not have an alternate method of obtaining a sufficient quantity of volume data. A survey was designed, but was not tested, because it was decided to survey travelers on I-80 rather than Route 85 as initially planned in order to use the survey to explain whatever differences were observed and to provide information on the extent to which the travel time savings motivated changes in job or housing location. The statistical analysis of changes in VMT based on Smog Check data did not prove feasible because the data were not available at a level of aggregation needed for such an analysis. Key word: effects of capacity increases, induced demand, latent demand