Evaluation of NDGPS for Assessing Road User Charges

With advances in modern technology, fuel consumption will drop with a resulting decrease in state and federal income from motor fuel taxes, decreasing the revenue available to maintain and improve the transportation infrastructure. To keep pace with future transportation needs, a new funding mechanism is needed to supplement or replace the current road financing mechanism. One possible approach is to charge for road use based directly on a measure of travel on public roadways. The main goal of this research was to develop the system requirements for the GPS component which would determine the vehicle’s location within an in-vehicle road user charging system. The focus was to evaluate the GPS in the most difficult of environments where roads of different jurisdictions and possibly different fee structures are located in close proximity to each other. In order for the system to be effective it must be able to place the vehicle on the correct road. Commonly used GPS receivers do NOT have sufficient accuracy for road user charging applications in which roads close to each other must be distinguished. However, GPS-determined positions can be corrected using differential GPS (DGPS). This paper describes (1) a methodology to specify the needed accuracy of a GPS receiver to meet a required accuracy in distinguishing roads with a given separation distance at a statistical level of confidence, and (2) the results of a series of road based experiments that were performed to evaluate GPS receivers that utilize the Nationwide DGPS (NDGPS) Service.