SAFE DRIVING ASSISTANCE SYSTEM AND IN-VEHICLE UNIT

A stopped vehicle cannot transmit position information about a subject vehicle by disabling communication. The vehicle-to-vehicle communication cannot therefore detect the position information about the stopped vehicle. A safe driving assistance system includes a first vehicle, a second vehicle, and an infrastructure. The second vehicle can transmit and receive position information from the first vehicle each other. The infrastructure includes a roadside unit that can receive position information about the first vehicle and position information about the second vehicle, can transmit position information about the first vehicle to the second vehicle, and can transmit position information about the second vehicle to the first vehicle. The infrastructure detects that the first vehicle stops, based on communication with the first vehicle, and transmits position information about the stopped first vehicle to the second vehicle.