In this thesis, a system for GPS positioning augmented with Ultra-Wideband (UWB) ranges for vehicle relative positioning applied in Vehicle-to-Infrastructure (V2I) navigation is developed and tested. It is assumed that UWB ranging information and carrier-phase differential GPS (DGPS) corrections are only available via a limited-range communication link between the vehicle and the infrastructure points. The navigation solution is implemented in an extended Kalman filter where differential GPS pseudorange, Doppler and carrier phase measurements are used in conjunction with UWB ranges measured between the vehicle and infrastructure points purposefully chosen on the road. Results indicate that the GPS and UWB integrated positioning system can improve the float solution and ambiguity resolution compared to the GPS-only case. When a single UWB radio is located roughly 300 m north of a fictitious intersection in 25 out of 40 cases the RMS position errors improved before the vehicle approaching the intersection. The inclusion of UWB ranges also improves in the time to fix ambiguities by 4.1% (0.4 seconds), 9.4% (0.9 seconds), 16.8% (2.4 seconds), 16.9% (3.2 seconds) and 15% (4.0 seconds) when the additional UWB measurements are available for 25 m, 50 m, 100 m, 200 m, and 300 m, respectively.