On the Road

Red light. Green light. Whoops, red light!

September 26, 2012

Anyone who has ever thumped his or her steering wheel in frustration at a green light turning red for no apparent reason just as you approach an intersection will appreciate this recent achievement from Carnegie Mellon University.



Researchers and engineers at Carnegie Mellon University have developed a high-tech traffic signal timing system that automatically adjusts and coordinates signal timing at adjoining intersections to accommodate varying traffic volumes. A pilot project in the Pittsburgh neighborhood of East Liberty has shown a reduction in vehicle wait times of 40%, a reduction in travel time through the area of 26% and a decline in exhaust emissions of about 21%.

This a quantum leap beyond simply synchronizing traffic signals -- which in itself isn't as easy as it might seem. Synchronizing traffic signals on a stretch of roadway will improve traffic flow as long as traffic remains within the timed parameters. If cars go too fast, they'll hit a red. If they go too slow, they'll eventually hit a red. On top of that, the greater the distance between the signals, the greater the likelihood that vehicles speed out of the sync timing. And sync'ing the lights only works in one direction; the cross streets don't see the benefits.

It's costly too. In the past, the signals had to be hard-wired together and timed from a single location. There are advantages to wireless communications between the signals, but that adds cost, too.

The system developed by CMU is not only very cost effective, it uses road loop sensors and cameras to gauge traffic flow so it can adjust the timing of the lights accordingly.

A report published by the Pittsburgh Post-Gazette pegs the cost of the system -- used to manage traffic at nine intersections -- at a mere $150,000. In 2011, the Washington State Department of Transportation estimated that the benefit-cost relationship of simple traffic synchronization as 40:1, so the cost benefit to the CMU system could be exponentially higher.

The paper reports Allen Biehler, executive director of CMU's University Transportation Center and former state secretary of transportation, called the results of the pilot project "startling" -- a word you don't often hear from bureaucrats.

Why Do They Do That?

I really welcome such developments. In my 2 million miles of big-truck travel around North America, I've come across some incredibly stupid traffic light systems. Some even appear to have been set up to deliberately thwart rather than improve traffic flow.

One of the worst is Tomken Road in Mississauga, Ontario.

It's a north/south artery running parallel to a major artery called Dixie Road in the heart of the city's industrial and warehousing area. During the day, you don't notice the problem, but after hours and especially in the wee hours of the morning when there's little traffic on the road, the lights will drive you to distraction.

The lights are generally green, and of course the side roads see red lights. Sitting on such a side road, facing a red light, you'll wait and wait and wait for the light to change -- until a vehicle approaches on Tomken, the main road. The approaching vehicle triggers something, causing its light to turn red and forcing it to stop, while the side street gets a green. Until a vehicle approaches on Tomken, the side street will not get a green. How can you explain that?

Another street in an industrial section of Toledo, Ohio, has synchronized signals, but nobody knows about them. Somebody on a CB told me if you run along the road at 35 mph (5 mph above the speed limit, oddly) you can skip all the way through about 15 traffic light without fear of hitting red. It won't work in a loaded truck from a stop, but if you hit the first light green and you maintain a steady speed, you're golden. There are no signs advising motorists of this well-kept secret. Why not? If everyone kept a steady speed going through town, they stand a better chance of making across in better time. It would cut down on speeding too. Surely that's an advantage.

The area of the CMU pilot project, Penn Circle in East Liberty, Penn. is -- or was -- a nightmare too. You could once be assured of hitting every light on the road red if you were in a truck. I don't know if the lights were timed to stop trucks, but they were very effective at that task. Given the emissions and congestion caused by trucks in stop and go traffic, I can't imagine a more poorly conceived traffic set up.

But that's all changed now.

A World Leader in Traffic Control

CMU's Traffic21 Initiative is much more complex than existing synchronized signal systems. The adaptive signal system uses concepts from the fields of artificial intelligence and traffic theory to fine-tune green light lengths in real time to best accommodate vehicle flow, writes Don Hopey of the Post-Gazette. Then, it relays those changes in real time to system sensors at neighboring intersections in the urban street grid.

The next phase of the project will be to expand the area served by the system and see how well in can manage a larger area with denser and more complex traffic patterns.

Presuming that proves successful, the world could be CMU's oyster. Cities and municipalities around the country and indeed the world would clamor for an inexpensive, highly adaptable and apparently very efficient traffic management system.

The Washington State Department of Transportation estimates benefit-cost relationship of adding one new lane of travel in each direction to a roadway at 10:1 -- assuming it can be done at all. No city in the world is going to tear up sidewalks to make way for wider roads, to even that relatively poor return isn't an option. CMU's system could offer an exponentially better return on the investment.

I can't wait to see where this goes from here.

Read the full Post-Gazette story here.

Check out this video to see how much better traffic flow can be with a little optimization.

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