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A green wave occurs when a series of traffic lights are coordinated to allow continuous traffic flow over several intersections in one main direction.
Any vehicle traveling along with the green wave will see a progressive cascade of green lights, and not have to stop at intersections. This allows higher traffic loads, and reduces noise and energy use. In practical use, only a group of cars can use the green wave before the time band is interrupted to give way to other traffic flows.
The coordination of the signals is sometimes done dynamically, according to sensor data of currently existing traffic flows - otherwise it is done statically, by the use of timers. Under certain circumstances, green waves can be interwoven with each other, but this increases their complexity and reduces usability, so in conventional set-ups only the roads and directions with the heaviest loads get this preferential treatment.
In 2011, a study modeled the implementation of green waves during the night in a busy Manchester suburb using S-Paramics microsimulation and the AIRE emissions module. The results showed using green wave signal setups on a network have the potential to: