STREETS & HIGHWAYS/Message signs reduce road’s collision rates

The California Department of Transportation’s District 2 knew it had a problem with a 30-mile stretch of the Sacramento River Canyon section of I-5. The highway runs through mountainous terrain, has a narrow median and features five curves that are virtual booby traps for the commercial tractor-trailers that travel the highway regularly.

Reducing the collision rate on that stretch of I-5 was important for a number of reasons, according to District 2 Deputy Director Russ Wenham. For one thing, I-5 is the primary route connecting the Pacific Northwest with central and southern California, and the Sacramento River Canyon stretch is particularly remote. “As remote as it is — and as narrow as the highway is, an accident can plug the freeway for many hours,” Wenham says. When that happens, traffic is basically stuck, since the nearest detour, unavailable in winter, means turning a one-hour trip into a five-hour trip.

So when District 2 personnel read a federal publication about rural ITS projects that cited a similar problem and solution in Colorado, their interest was piqued. Using information from the Colorado project, District 2 began a pilot project in 1999 designed to reduce the number of accidents on the canyon highway. The project involved the placement of LED, changeable message signs (CMSs) that contain radar units. The units judge the speed of the largest approaching vehicle and display it, along with information about the highway ahead.

Because interactive warning signs were not on the list of traffic control devices approved by the state’s Traffic Control Devices Committee, the project was designated an Experimental Feature Project. The system was designed in-house by District 2 employees, who wrote specifications that would allow for as much off-the-shelf technology as possible.

Each 7-foot-by-10-foot CMS displays truck speed, the speed suggested for the curves ahead and graphics that show the layout of the next section of highway. With a range of 5 feet to 7,250 feet, the radar is accurate to ±1 mile per hour.

The district’s management center in Redding monitors each sign via a standard 56K analog modem. Additionally, two traffic surveillance closed-circuit television cameras monitor each CMS location, one directed at approaching traffic and the other at departing traffic.

The project has been a resounding success, Wenham says. “We were averaging a cumulative 7.5 truck accidents a year at the five locations before we put up the signs,” he says. “In the first 14 months with the signs, there were only two truck accidents. All accidents have gone down, but truck accidents have really dropped.”

People are noticing, Wenham says. “Someone this morning caught me and said that, over the weekend, he was driving through the canyon, and it was interesting to watch truckers put on their brakes and slow down as they approached the signs,” he says. “We’ve gotten a lot of positive feedback. It’s one of the few projects we have done that generates this much feedback.”

For information on the project, contact Wenham at (530) 225-3545 or at russ.wenham@dot.ca.gov.