Abstract: An on-board unit 1 mounted on a vehicle includes a GPS receiver 21 determining the location of the on-board unit 1, a radio communication interface 22 and a processing unit 25. The processing unit 25 is configured to generate vehicle location information indicating the location of the on-board unit 1 determined by the GPS receiver 21 after starting a normal operation and to transmit the vehicle location information to the external device with the radio communication interface 22. The processing unit 25 is configured to, when detecting a stop of the vehicle, transmit vehicle stop information indicating the stop of the vehicle to the external device with the radio communication interface 22 and to place the on-board unit 1 into a low power consumption state after the transmission of the vehicle stop information.

Abstract: A traffic information processing system includes on-board unit configured to be installed in a vehicle, an on-board unit-equipped vehicle number-detecting unit configured to detect the number of vehicles equipped with on-board unit entering a sample area based on information received from the on-board unit, a total vehicle number-detecting unit configured to detect the number of all vehicles entering the sample area, a vehicle ratio operation unit configured to calculate a value related to a ratio based on the number of vehicles equipped with the on-board unit detected by the on-board unit-equipped vehicle number-detecting unit and the number of all vehicles detected by the total vehicle number-detecting unit, and a total vehicle number-estimating operation unit configured to calculate a total number of vehicles in the zone.