Concept
A green wave occurs when 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 traveling along with the green wave (at an approximate speed decided upon by the traffic engineers) 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 (because less acceleration and braking is needed). In practical use, only a group of cars (known as a "platoon", the size of which 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 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 (Chorlton-cum-Hardy) using S-Paramics microsimulation and the AIRE emissions module. The results showed using green wave signal setups on a network have the potential to: Reduce CO2, NOx and PM10 emissions from traffic. Reduce fuel consumption of vehicles. Be used on roads that intersect with other green waves. Reduce the time cars wait at side roads. Give pedestrians more time to cross at crossings and help them to cross streets as vehicles travel in platoons Control the speed of traffic in urban areas. Reduce component wear of vehicles and indirect energy consumption through their manufacture A green wave in both directions may 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.