A vehicle line-of-sight optical communication system and method for use in ad hoc networks formed with a vehicle during traveling of the vehicle along a roadway. The communication system includes: an electronic control unit (ECU) having an electronic processor that operates under control of a program to process messages sent or received by the communication system; at least one light source that comprises a part of a vehicle external lamp module; a driver circuit electrically connected to the ECU to energize the light source(s) in response to a transmission signal from the ECU so as to send messages via the light source(s); at least one light sensor that comprises a part of the vehicle external lighting system; and a receiver circuit electrically connected to the ECU to provide the ECU with a reception signal indicative of messages received via the light sensor(s).