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Open Access Publications from the University of California

Whence Induced Demand: How Access Affects Activity


Additional highway capacity, by increasing travel speed, affects the individual share of time within a 24-hour budget allocated to various activities (time spent at and traveling to home, shop, work and other), some activities will be undertaken more, others less. This paper extends previous research that identified and quantified induced demand in terms of vehicle miles traveled, by considering questions of what type of demand is induced and which activities are consequently reduced. This paper uses the 1990 and 1995 Nationwide Personal Transportation Survey and Federal Highway Administration highway statistics data. While total travel times have not seen any significant change between the years 1990 and 1995, there is a significant change in activity durations. Further, as a result of additional capacity, workers spend less time traveling. Workers also spend more time at home and other activities and less at work and shop. Non-workers, in contrast, travel more, and spend more time shopping and at home, but less time at other activities. This points out the differences in discretionary and non-discretionary activities for workers and non-workers. It also suggests that there are real gains from capacity in people's lives, at least in the short term, as it is time, and not VMT, that individuals base decisions on.

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