Green wave

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A green wave is an intentionally induced phenomenon, where a series of traffic lights (usually three or more) are coordinated to allow continuous traffic flow over several intersections in one main direction.

Any vehicle travelling along with the green wave (at an approximate speed decided upon by the traffic signal designers) will not have to stop at intersections. This allows higher traffic loads, and reduces noise and energy use (because less acceleration and braking is needed). In practical use, only a group of cars (the size is defined by the signal times) 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 only the roads and directions with the heaviest loads get this preferential treatment.

A green wave has a disadvantage that motorists slower than the recommended speed may reach a red signal at the traffic lights, and a large queue of traffic may build up behind them thus ending the wave. Racing motorists also hold up the wave because when they reach the traffic light it may be a red signal, and it may take a while for them to reach the speed of the wave that will be coming from behind them when the traffic light turns to green. These problems can partly be avoided by monitoring of disobedient motorists.

A green wave in both directions may only be possible with different speed recommendations for each direction, otherwise traffic coming from one direction may reach the traffic light faster than from the other direction if the distance from the previous traffic light is not mathematically a multiple of the opposite direction.

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