In-vehicle signing in the United States : using an existing system with 20 million receivers already in use in the highway infrastructure.

An in-vehicle highway hazard safety warning system has been developed by the Georgia Tech Research Institute (GTRI), working under the sponsorship of the Safety Warning Foundation L.C., to alert motorists of highway hazards. The system alerts motorists who own one of the estimated 20 million radar detectors already in use on the highways of the United States. Motorists using police radar detectors built before January 1, 1997 will get an alert when they are near a safety warning transmitter. All detectors built by the participating manufacturers after January 1, 1997 will display a specific safety warning alert and, in the more expensive detectors, one of 64 fixed text highway safety warning and information messages on an alphanumeric display and, in at least two models, a voice synthesizer. The Safety Warning System (SWS) consists of a roadside or vehicle mounted transmitter and the detector display unit. The mobile transmitter can be mounted on police cars, emergency vehicles, utility vehicles, and highway repair vehicles. The fixed site transmitter is designed to be placed at periodic locations along the highway. The reception range of the transmitted signal is between 0.8 and 2.4 kilometers, depending on terrain.