Optimal route computation is one of the important function of many GIS, especially transportation applications. The GIS component of Autonomous Route Management and Guidance Systems (ARMGS) requires this computation in real-time and usually contains a large road network with some constraints. The existing algorithms for computing optimal routes do not meet all of these requirements, thus alternative algorithms are needed. A heuristic algorithm is seen as an alternative which meets the stated requirements. In this paper, a heuristic algorithm for computing optimal routes is described. Furthermore, this algorithm is compared with other algorithms and approaches.