Worker Warning Device: Intrusion Alarm Technical Information

This article discusses the various technologies used to develop intrusion alarms which warn maintenance workers of moving vehicle intrusion into a work zone. The warning devices were initially developed by the Strategic Highway Research Program (SHRP) using ultrasonic and infrared technologies. A detection/transmitter device is placed “upstream” of the workzone while a receiver with a siren is placed near the work zone. The alarm is triggered when the infrared beam or sound signal is interrupted. Since the development of this “first generation” intrusion alarm, manufactures have used other technologies to develop other similar devices. Brief descriptions of the systems using various technologies are given. The pressure-activated alarm uses a pneumatic tube, pressure switch, rechargeable battery and radio transmitter. The infrared alarm system uses a transmitter with an infrared beam directed toward a receiver unit. The microwave alarm operates similarly to the infrared alarm except that it uses microwaves. Finally, the ultrasonic alarm uses sound waves in the anon-contact method of vehicle detection. Alarm system setup is also briefly described.