In 2004 the Illinois Department of Transportation deployed two self-contained vans to implement a legislatively mandated speed-radar photo enforcement (SPE) program in work zones on highways. The speeds of vehicles approaching the SPE vans are monitored with two radar systems: down-the-road radar and across the-road radar. The speed obtained from the down-the-road radar is displayed on a light-emitting diode display on top of the SPE van. The display gives speeding drivers a final chance to reduce speed and comply with the work zone speed limit. If the speed of the vehicle, measured by across-the-road radar, is greater than a specified value, the two onboard cameras are activated to take pictures of the driver and the rear license plate of the vehicle.
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