Without doubt the single most aggravating system in metropolitan areas is the roadway control by traffic signals.  Traffic jams and road congestion do a lot more than disrupt the lives of millions of people every day – in the United States alone, delays linked to backed-up traffic cost nearly $100 billion each year, and waste more than 2.5 billion gallons of fuel, not to mention the uncountable human hours – some of them yours.

The popular idea is build more roads, or encourage more people to ride bikes or share their cars with others, and improve buses and other forms of public transport.  BUT!  How about another way – organize the signals!

Stefan Lämmer at the Institute of Transport & Economics of TU Dresden and Dirk Helbing of ETH Zurich have recently shown organization could reduce traffic congestion markedly by re-thinking the way we try to control how traffic flows.  Three Cheers for the Innovators!

The idea today is that lights should cycle on and off in a regular and predictable way, but this idea, the pair says is unnecessarily restrictive. And less orderly patterns could be far more efficient, reducing travel times for all, and making traffic jams far less frequent.

Currently traffic engineers normally tailor the cyclic operation of signal lights to match known traffic patterns from the recent past. Lights on main roads stay green longer during peak hours, for example. But so far it requires supercomputers or engineers to do the tuning.

Lämmer and Helbing wondered if traffic lights might devise better solutions on their own, if given some simple traffic-responsive operating rules and left to organize their own on-off schedules. To find out, they modeled the flow of traffic as if it were a fluid, and explored what happens at road intersections, where traffic leaving one road has to enter another, much like fluid moving through a network of pipes.

Traffic Signal Flows Compared. From the working paper. Click the image for the largest view.

In principle, if traffic entering a road overloads its capacity jams obviously arise. To avoid this, Helbing and Lämmer gave each set of lights sensors that feed information about the traffic conditions at a given moment into a computer chip, which then calculates the flow of vehicles expected in the near future. It also works out how long the lights should stay green in order to clear the road and thereby relieve the pressure. In this way, each set of lights can estimate for itself how best to adapt to the conditions expected at the next moment.

Lämmer and Helbing found this simple rule isn’t enough: the lights sometimes adapt too much. If they are only adapting to conditions locally, they might stay green for too long and cause trouble further away. To avoid this the pair modified things so that what happens at one set of traffic lights would affect how the others respond. By working together and monitoring the lengths of queues along a long stretch of road, the self-organized lights prevent long jams from forming.

As simple as they seem these rules seem to work remarkably well. Computer simulations demonstrate that lights operating this way would achieve a significant reduction in overall travel times and keep no one waiting at a light too long. One of the biggest surprises, however, is that all this improvement comes with the lights going on and off in a seemingly chaotic way, not following a regular pattern as one might expect.  Try that with a supercomputer or as an engineer working in real time.

The key is that this kind of control does not fight the natural fluctuations in the traffic flow by trying to impose a certain flow rhythm from regular signal cycling.

Instead the rules exploit randomly appearing gaps in the flow to serve other traffic streams. According to the simulations, this strategy can reduce average delay times by 10% to 30%. Remarkably, the variation in travel times goes down as well, although the signal operation tends to be non-periodic and, therefore, less predictable. You can’t say precisely how the lights will go on and off, but you can be sure your drive will be shorter.

Sign my city up.

Helbing points out, the scheme eliminates other irritating problems, such as drivers having to wait a long time at empty intersections because the signal schedules are determined by the traffic flow at busier times, or lights cycling even in the middle of the night when there is no need. The self-organizing traffic scheme eliminates these problems because the lights remain responsive to local demands, for instance sensing an approaching car and changing to green to let it through.

Please sign my city up!

City planners in Germany are beginning to look at self-organizing lights as a practical solution to looming traffic congestion. Lämmer and Helbing are working with a German traffic agency to implement the idea. In previous tests based on Dresden’s road layout, they’ve had encouraging results.

These scientists have their working paper available in a pdf file available for download.  Its something you might want to look over and pass along to your local officials.

Argh.  One can hope these two fine innovators get a call from a commercial venture that would promote the system worldwide.  This writer hasn’t been in any area, urban or suburban that can’t use a massive improvement on signal operation.  After all, how much could it cost?  The first rule would work well in less dense areas negating the need for a full organization effort and the communication needs as density increases might be quite low cost with the available systems today.

Meanwhile, as you gnash those teeth, keep in mind the solution is out there.  That’s enough to really upset a time pressured driver.


4 Comments so far

  1. JPK on September 23, 2010 8:57 PM

    Remember what people like me need to remain patient when there is traffic: good discpline plus a hefty dose of technological blessings in disguise are among the measures at our disposal – appropriately enough in any situation around the globe. That is what people must do in dealing with traffic situations along the various streets and highways. Any more suggestions please?

  2. Edgar Deroberts on May 26, 2011 10:19 AM

    I REALLY liked your post and blog! It took me a minute bit to find your site…but I bookmarked it. Would you mind if I posted a link back to your post?

  3. Jeff Olive on September 1, 2011 10:06 PM

    I would like to say “wow” what a inspiring post. This is really great. Keep doing what you’re doing!!

  4. Evan Precht on September 8, 2011 7:07 PM

    Great read. Thanks for the info!

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