In this paper, we study the shortest route service on Intelligent Transportation System (ITS) which provides the shortest route between two locations specified by a mobile client. We discuss the traditional dedicated channel method and propose a new on-demand broadcasting method. Three measurements are considered when analyzing and simulating the above two methods: (1)the total channel cost (i.e., the amount of data sent from the server), (2) the system time (i.e., the time elapsed between the issuing and termination of a request), and (3) the channel interference. The results show that our on-demand broadcasting method yields less total channel cost for the same group of mobile clients and less system time. Furthermore, as the cell radius increases, the channel interference caused by the broadcast channel increases.