The main goal of this research was to develop the system requirements for the global positioning system (GPS) and the digital map components that make up the core of an in-vehicle road user charging system. The focus was to evaluate both GPS and digital maps in the most difficult of environments - where roads of different jurisdictions and possibly different fee structures are located in close proximity to each other (a highway and a frontage road, for instance). In order for the system to be effective it must be able place the vehicle on the correct road. GPS receivers that are commonly used by automotive navigation systems do not have sufficient accuracy for road user charging applications. However, the GPS-determined positions can be corrected, and thus made more accurate, using publicly and privately available wireless signals, namely, using differential GPS (DGPS). This experimental study, based on road testing, found that only certain DGPS receivers are capable of achieving the needed accuracy. Extensive testing of existing digital maps found that they are also not accurate enough to be used for road user charging. There are however, new, higher accuracy digital maps (not yet publicly available) that are already being used for vehicle safety applications. By combining DGPS and such high accuracy digital maps, the ability to design a road user charging system with high geographical resolution can become a reality.