New software alleviates traffic - Transportation

The same in-road detectors that control traffic lights and monitor traffic could soon respond quicker to traffic jams, thanks to software developed by Benjamin Coifman, assistant professor of electrical engineering and civil and environmental engineering, Ohio State University, Columbus. In tests, the software helped California road crews discover traffic jams three times faster than before, allowing them to clear accidents and restore traffic flow before many other drivers would be delayed. This technology also could provide drivers with the information they need to plan efficient routes, and even improve future road design.

Many drivers probably have noticed the buried devices, called loop detectors, at intersections. A square outline cut into the pavement marks the spot where road crews have inserted a loop of wire. When a car stops over the loop, a signal travels to a control box at the side of the road, which tells the traffic light to change. Although the loop detectors are barely more than metal detectors, they collect enough information to indicate the general flow of traffic, Coifman explains. So, he set out to use the detectors to pinpoint traffic congestion and accurately measure vehicles' travel time.

With the software, a small amount of roadside hardware, and a single PC, a city could improve traffic monitoring significantly without compromising drivers' experience of the road, Coifman concludes. That's important, he argues, because good traffic management can't be obtrusive. "If transportation engineers are doing their job well, you don't even realize they've improved travel conditions."

Coifman wrote computer algorithms that can capture a vehicle's length as it passes over a detector. Once a vehicle of similar length passes over the next loop, the computer could match the two signals and calculate the vehicle's travel time. Based on each car's travel time, the software was able to determine within three and a half minutes after traffic began to slow that a traffic jam had formed. Because drivers' behavior isn't predictable, the new algorithms had to take many human factors into account. Coifman had to consider people changing lanes, entering and exiting from ramps, rubbernecking, etc. "Traffic is a fluid like no other fluid," he suggests. "You can think of cars as particles that act independently, and waves propagate through this fluid, moving with the flow or against it."

After an accident, it may take a long time for the telltale wave of slow-moving traffic to propagate through the detectors. With the new algorithm, Coifman can detect delays without waiting for slowed traffic to back up all the way to a detector. This improved response time is important, because the personal and financial costs grow exponentially the longer people are stuck in traffic.

The average American city dweller wastes 62 hours per year stuck in traffic, according to the 2002 Urban Mobility Study by the Texas Transportation Institute, which measured traffic delays in 75 major cities. According to the same study, traffic jams cost the average city $900,000,000 in lost work time and wasted fuel every year.

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