ICT researchers prove benefits of speed photo-radar enforcement in work zones

Between 6,000 and 7,000 crashes occur in Illinois' work zones annually. Contrary to popular belief, motorists are more likely to get hurt in work zones than workers; motorists account for approximately 85% of the total injuries and fatalities in work zones.

To encourage slower, and therefore safer, driving in work zones, Illinois enacted the Automated Traffic Control Systems in Highway Construction or Maintenance Zones Act in 2004. This act authorized the use of the SPE van in work zones for the first time in the United States. But although this method of SPE has been used in Illinois since 2004, its effects had until recently gone unstudied.

Rahim Benekohal, a professor of civil and environmental engineering at Illinois, along with his student researchers Ali Hajbabaie, Juan Medina, Ming-Heng Wang, and Madhav Chitturi evaluated the effects of the SPE on speed and degree of speeding in work zones and compared them to the results from other speed-control methods that included law enforcement presence in work zones.

How Does SPE Work?

SPE uses vans equip with radar and cameras to monitor the speeds of approaching vehicles. The speed obtained displays on top of the SPE van, which gives speeding drivers one last chance to reduce their speeds and comply with the speed limit. If the driver does not reduce his or her speed, a camera captures the face of the driver and the front license plate. The SPE also records the speed of the violator, date, location, and time of the violation.

The vans are staffed by Illinois State Police officers who can issue a citation for speeding vehicles if he/she decides it is a clear case of excessive speeding. First, the officer identifies the vehicle's owner from the license plate of the speeding vehicle. The picture of the speeding driver is compared to the owner's picture in the driver's license database. Currently, if the picture of the driver at the time of the violation matches the picture of the registered owner of the vehicle, the ticket is approved. The citation is mailed to the registered owner of the vehicle within 14 business days.

How Does SPE Effect Drivers?
The ICT researchers compared the effects of the SPE on mean speed and degree of speeding to the conditions without police presence and to some variations of police presence in the work zone. They studied the effects of different treatments on cars and trucks separately, free flowing and general traffic stream vehicles, and on the median (passing lane) and the shoulder lane (driving lane).

In most cases, the investigators found that the SPE was just as effective in reducing drivers' speeds as having a police car with its flashing lights off present in the work zone. The SPE lowered the average speed of the general traffic stream below the speed limit in all cases.

"SPE was very effective in reducing the average speed of cars and trucks, thus calming traffic and improving safety in work zones," explained Benekohal, whose research includes traffic flow modeling and simulation, traffic flow theory, intelligent transportation systems, traffic operations, and traffic safety. He also teaches undergraduate and graduate courses on campus.

The research found the reductions to be significant. When the SPE was present, on average, cars traveled 5.1-8.0 mph slower in the median lane and 4.3-7.7 mph slower in the shoulder lane."