A system located in an automobile provides personalized traffic information nd route planning capabilities. This system uses equipment which is becoming standard in automobiles, such as on-board navigation systems and cellular telephones. On-board navigation systems use global positioning system (GPS) satellites to position the automobile with respect to streets in a map database. As the automobile moves, the navigation system updates the location. A central database includes travel time information for each street segment and transition between street segments in the map database. Based upon the travel time information in the database, a route from a current location to a desired destination, or series of destinations, can be planned in order to have a minimum travel time. The route can be provided to the on-board navigation system, which then directs the driver in traveling the route. The cellular telephone in the automobile can be used for communicating with the central database to obtain travel times for route planning. In order to provide dynamic travel time information to the central database, each automobile in the system operates as a data collector. As various street segments are traversed, the travel time for each segment is recorded. The travel time and street segment information is periodically transferred to the central database through the cellular telephone connection. The central database then combines the travel time data from each automobile to create accurate travel time data for each street segment.