Adaptive
lights organize traffic
By
Kimberly Patch,
Technology Research NewsTraffic is notoriously difficult to predict because it's a complicated system involving many vehicles, many people's behavior, and constant changes. If a single car takes more time than expected to start up at a green light, the cars behind will be delayed. Put a few such delays together and you have traffic jam, never mind traffic-altering variables like weather, roadworks, sports events, concerts and holidays.
Traffic lights that adapt to traffic flow are currently in use, but often consist of relatively expensive equipment including a control center that receives information from traffic lights and sends back appropriate instructions.
A researcher from the Free University of Brussels (VUB) in Belgium has devised a way to allow traffic lights to self-organize to improve traffic flow. The method, which taps the self-organizing principles of social insects, does away with central control.
Traditionally, traffic lights are optimized using computational methods that find appropriate periods and phases of traffic lights, said Free University of Brussels researcher Carlos Gershenson. But traffic flow is less an optimization problem than an adaptation problem because traffic flows and densities change constantly, he said.
In Gershenson's relatively simple simulations, traffic lights were able to self-organize and adapt to changing traffic conditions, reducing wait times and increasing average speeds compared to a pair of traditional traffic-management methods. An increase in average speed shows that cars are spending less time stopped at lights.
The method is based on a fairly simple approach used in England for coordinating traffic at isolated intersections, said Gershenson. A red light keeps track of the number of cars approaching it and multiplies that number by time increments. When the result reaches a certain threshold, the traffic light changes. The more cars approaching or waiting at a red light, the faster it will turn to green.
The traffic light pattern encourages cars to form platoons, which improve average speeds. This method works well when traffic is light, but in heavy traffic the method does not work because the threshold is reached very quickly, and the lights change constantly.
Gershenson adapted the method to make it work in heavy traffic by adding a constraint: a green light cannot be switched red before a minimum period.
Other researchers have developed traffic management schemes that call for traffic lights to communicate with each other.
Under the Free University of Brussels scheme, the traffic lights cannot communicate directly with each other, but reacting to local traffic density allows them to coordinate indirectly. "They communicate indirectly through their environment, as many social insects do," said Gershenson. "The environment of the traffic lights [is] the cars."
The method allows the traffic lights to exploit the environmental information -- cars -- to self organize. "There is no need of the central command center, communication between agents, nor hierarchies," said Gershenson.
It remains to be seen which approach works better in which situations, said Gershenson.
Gershenson's simulations represented traffic flow in a 10-by-10 grid of one-lane roads of alternating directions. They allowed more cars flowing in a particular direction to simulate rush-hour traffic. Cars could go straight or turn at an intersection.
The simulation varied the number of initial cars among 10, 20, 40, 80, 160, 360, 640, 1,280 and 2,560. Gershenson took the averages of 20 runs lasting 10,000 time increments each.
Gershenson's next steps are to put the idea through more complicated simulations that consider pedestrians and left hand turns, run a pilot study, and compare it with current adaptive traffic management systems.
The system could be applied practically in less than two years, according to Gershenson. The research was funded by the University.
Timeline: > 2 years
Funding: University
TRN Categories: Multiagent Systems; Applied Technology
Story Type: News
Related Elements: Technical paper, "Self-Organizing Traffic Lights," posted on the arXiv physics archive at xxx.lanl.gov/abs/nlin.AO/0411066; self-organizing traffic lights simulation posted at homepages.vub.ac.be/~cgershen/sos/SOTL/SOTL.html
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January 26/February 2, 2005
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Adaptive lights organize traffic
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