Battling traffic jams with smarter traffic signals

Traffic jams are annoying and costly, and cities are using vigorous and various means to relieve their car-clogged roads.

Many of these efforts focus on thinning out the number of drivers by promoting mass transit use, carpooling and ridesharing -- or finding ways to make driving unappealing.

As it turns out, getting traffic signals to perform better may offer the most immediate help for traffic jams. Today’s traffic management systems are leveraging road-embedded sensors and software systems to more quickly adjust signal timing and, in the process, improve traffic flow.

Los Angeles, the U.S. traffic congestion king, is the poster child for automated traffic control systems. Using data from an array of magnetic road sensors and hundreds of cameras, a centralized computer system controls 4,500 traffic signals throughout  the city in an effort to keep traffic moving. Completed two years ago, the $400 million system is credited with increasing travel speeds around the city by 16%, and shortening delays at major intersections by 12%.

Getting the timing down in Minnesota

But smaller and less ambitious approaches are generating results, too. One example is SMART Signal, a University of Minnesota research project funded by the Minnesota Department of Transportation.

The SMART Signal system addresses the issue that loop detectors embedded in Minnesota state, county and city roads only notify a traffic signal that a vehicle is present. Typically, transportation staff must manually track wait times to determine how the signal timing is affecting traffic. Because such manual tracking is a time-consuming and costly process, re-timing traffic signals lags behind and doesn’t sync with the changing traffic volumes on the streets.

SMART Signal remedies this problem by automatically recording the vehicle wait time and reporting that data to a central server. There it is analyzed and the timing plan for under-performing traffic signals is updated with little human intervention. The system has reduced traffic delays by 5% in one test.

“Data collection and performance monitoring are critical for improving traffic signal operations, and yet before the development of the SMART Signal system, these tasks were prohibitively expensive for most agencies because of the number of signals involved,” noted principal investigator Henry Liu.

Analyzing driver behavior

While the Minnesota project represents a step-up in traffic signal automation, traffic engineers and researchers envision still more advanced Internet of Things-based solutions that extend traffic control systems beyond specific traffic corridors and networks.

“The technologies to deal with complex environments ... are only starting to mature now — combining the ability to adapt signal timing to more sophisticated predictive analytics and real-time monitoring,” notes Matthew Cole, executive vice president for strategy, business development and diversification at Council Lead Partner Cubic Transportation Systems.

“Currently, the state-of-the-art is alternating lights in a fixed way according to the time of day," Cole explains. "The more sophisticated versions also use sensor data of traffic queues at intersections.”

Future traffic management systems might also provide insight into complex yet common problems such as how modifying one set of traffic lights affects other intersections -- and driver behavior, too.  A recent ACM article describes the work of Carolina Osorio, an MIT civil and environmental engineering professor, who is doing work along this line.

Osorio is evaluating a monitoring system and algorithms in Lausanne, Switzerland and New York City that use traffic simulators that analyze the behavior of drivers in response to changing conditions. She has found that in Lausanne, the testing has shown a 22% reduction in travel time compared to commercial software for traffic light timing.

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