In the Seattle metropolitan area, a congestion pricing project was conducted to examine the driving behavior of 275 volunteer households who had vehicles equipped with GPS tolling meters similar to those used in taxis. The overall goals of the project were to examine how road users responded to price, determine whether variable tolling was a useful approach to road finance and management, and demonstrate how proven technology can be used to implement tolling on large transportation networks without having to deploying substantial physical hardware at the roadside.
Between July 2005 and March 2006 the project observed participant driving patterns before and after hypothetical tolls were imposed on all major freeways and arterials in the Puget Sound region. The technology installed in each participant's vehicle recorded the vehicle's location and matched the vehicle's position to a map of toll roads within the tolling meter. During the before period, drivers were able to view an in-vehicle display that showed the name of the road they were traveling on. During the after period the display showed the name of the road as well as the toll rate per mile and the cumulative toll for the current trip. Periodically, the on-board unit would communicate to a central computer using a cell phone network and reconcile toll charges to each participants account.
To encourage participation, drivers were given an expense account from which to deduct toll charges. If any money remained in the account at the end of the study, the participants were allowed to keep it. The intention was to provide incentive to modify driver behavior and budget toll road use. A website was set up to allow participants to monitor their travel, reflect on trip choices, and gauge the overall consequences of those choices on their account balances.
The study identified a number of changes in aggregate travel demand of participants.
- 7 percent reduction in all vehicle trips per week.
- 12 percent reduction in vehicle miles traveled (VMT) per week.
- 8 percent reduction in travel time per week.
- 6 percent reduction in trip segments per week.
- 13 percent reduction in miles driven on tolled roads (tolled miles per week).
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