A vehicle tracking system includes a sensor (e.g., a GPS sensor) and a vehicle control unit (VCU) attached to a vehicle. The sensor determines the vehicle's location based on positioning signals received from a plurality of satellites. The VCU compares the vehicle's location to a predefined schedule. The predefined schedule includes a plurality of entries where each entry corresponds to a location along the vehicle's route of travel. Furthermore, each entry includes a location value indicating the location that corresponds with the entry and a time value indicating when the vehicle should be at the location. The VCU determines whether the vehicle is on schedule or off schedule by comparing the current location of the vehicle (as determined by the sensor) and the amount of time elapsed since the start of the route with the entries in the predefined schedule. If the vehicle is off schedule, then the VCU transmits a status message to a remote location indicating how much the vehicle is off schedule. A computer at the remote location is aware of the predefined schedule and assumes that the vehicle is on schedule unless a status message is received from the VCU. If a status message is received, the computer at the remote location determines the current location of the vehicle based on the status message.