Evaluation of a Radar Activated Horn System for Speed Control in Highway Maintenance Operations

This study evaluated the speed reduction effects of providing an audible message to the speeding motorists approaching a highway striping crew. The audible system consisted of a radar unit which activated a horn when approaching vehicles exceeded a speed threshold. Speed data for 118 vehicles were collected and a speed reduction profile for each vehicle was generated. The data were divided into horn activated, horn not activated, and control groups. When the horn was activated, the average, maximum, and minimum speed reductions were 9.71, 17, and 4 mph at a distance about 750 ft from the horn. When the horn was not activated the average, max and min reductions were 3.5, 5, and 3 mph, respectively. As the detection distance decreased, the effectiveness of the horn system decreased too. The exact amount of additional speed reductions due to horn blasts alone could not be determined because of a small control data. However, the range of the additional speed reduction due to the horn was estimated to be 0-6 mph at 750 ft from the horn, and 0-2 at 500 ft from the horn. At a distance 750 ft from the horn the speed reduction effect of the horn was the greatest. The horn should be activated when a speeding vehicle is at a distance not less than 750 ft from the horn to give the drivers enough time to slow down before passing the truck. The horn system seemed to have some speed reduction effects on the motorists. However, noise problems and the human factors considerations of this system needs to be studied. These concerns may limit application of this device to very special cases. Further studies on the effectiveness of the system are needed.