This paper describes the design of a macroscopic traffic simulator using Geographical Information System (GIS) and its implementation for performance evaluation of different IVHS route guidance strategies. The GIS and the associated routing algorithms are intended for deployment in the NY/NJ metropolitan area by TRANSCOM. The GIS allows flexible display of a host of traffic parameters and selection of control actions. Besides GIS and control algorithms, a simulator is implemented to replace the traffic measurements for secondary road network (or even the main traffic arteries in the early phase of the IVHS implementation). The role of the simulator as a tool for designing different control algorithms is also mentioned. The simulator operates by iteratively updating all the densities on all the included roads. The relations for each road are based on well known vehicular traffic models (such as Greenshield's). The dependence between the traffic parameters on different roads is incorporated via relations between a road's traffic parameters and those of its entrance and exit roads.