Green wave
Encyclopedia
A green wave is an intentionally induced phenomenon in which a series of traffic light
s (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 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 only the roads and directions with the heaviest loads get this preferential treatment.
A green wave has a disadvantage that slow drivers may reach a red signal at the traffic lights, with a queue of traffic may build up behind them, thus ending the wave. In general, stopping and then starting at a red light will require more time to reach the speed of the wave coming from behind when the traffic light turns to green.
Green waves are most effective with one-way traffic
. 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.
Green waves are sometimes used to facilitate bicycle traffic. Copenhagen
, Amsterdam
, San Francisco, and other cities, may synchronize traffic signals to provide a green light for a flow of cyclists. In Copenhagen, a green wave on the arterial street Nørrebrogade facilitates 30,000 cyclists to maintain a 12 mph (19.3 km/h) speed for 2.5 kilometers. In Amsterdam, cyclists riding at a speed of 15 to 18 km/h will be able to travel without being stopped by a red signal. Tests show that public transport can benefit as well and cars may travel slightly slower.
Frederiksberg
, a part of Copenhagen, the capital of Denmark, has implemented a green wave for emergency vehicles to improve the public services.
In the UK, it was revealed that the Department for Transport
had previously discouraged green waves as they reduced fuel usage, and thus less revenue was raised from fuel taxes.
Traffic light
Traffic lights, which may also be known as stoplights, traffic lamps, traffic signals, signal lights, robots or semaphore, are signalling devices positioned at road intersections, pedestrian crossings and other locations to control competing flows of traffic...
s (usually three or more) are coordinated to allow continuous traffic flow over several intersections
Intersection (road)
An intersection is a road junction where two or more roads either meet or cross at grade . An intersection may be 3-way - a T junction or fork, 4-way - a crossroads, or 5-way or more...
in one main direction.
Any vehicle travelling along with the green wave (at an approximate speed decided upon by the traffic engineers
Traffic engineering (transportation)
For the engineering of communications and computer networks, see Teletraffic engineering.Traffic engineering is a branch of civil engineering that uses engineering techniques to achieve the safe and efficient movement of people and goods on roadways...
) 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
Signal timing
Signal timing is the technique which traffic engineers use to determine who has the right-of-way at an intersection. Signal timing involves deciding how much green time the traffic lights shall provide at an intersection approach, how long the pedestrian WALK signal should be, and many numerous...
) 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 slow drivers may reach a red signal at the traffic lights, with a queue of traffic may build up behind them, thus ending the wave. In general, stopping and then starting at a red light will require more time to reach the speed of the wave coming from behind when the traffic light turns to green.
Green waves are most effective with one-way traffic
One-way traffic
One-way traffic is traffic that moves in a single direction. A one-way street is a street either facilitating only one-way traffic, or designed to direct vehicles to move in one direction.-General signs:...
. 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.
Green waves are sometimes used to facilitate bicycle traffic. Copenhagen
Copenhagen
Copenhagen is the capital and largest city of Denmark, with an urban population of 1,199,224 and a metropolitan population of 1,930,260 . With the completion of the transnational Øresund Bridge in 2000, Copenhagen has become the centre of the increasingly integrating Øresund Region...
, Amsterdam
Amsterdam
Amsterdam is the largest city and the capital of the Netherlands. The current position of Amsterdam as capital city of the Kingdom of the Netherlands is governed by the constitution of August 24, 1815 and its successors. Amsterdam has a population of 783,364 within city limits, an urban population...
, San Francisco, and other cities, may synchronize traffic signals to provide a green light for a flow of cyclists. In Copenhagen, a green wave on the arterial street Nørrebrogade facilitates 30,000 cyclists to maintain a 12 mph (19.3 km/h) speed for 2.5 kilometers. In Amsterdam, cyclists riding at a speed of 15 to 18 km/h will be able to travel without being stopped by a red signal. Tests show that public transport can benefit as well and cars may travel slightly slower.
Frederiksberg
Frederiksberg
Frederiksberg Kommune is a municipality on the island of Zealand in Denmark. It surrounded by the city of Copenhagen. The municipality, co-extensive with its seat, covers an area of and has a total population of 98,782 making it the smallest municipality in Denmark area-wise, the fifth most...
, a part of Copenhagen, the capital of Denmark, has implemented a green wave for emergency vehicles to improve the public services.
In the UK, it was revealed that the Department for Transport
Department for Transport
In the United Kingdom, the Department for Transport is the government department responsible for the English transport network and a limited number of transport matters in Scotland, Wales and Northern Ireland which are not devolved...
had previously discouraged green waves as they reduced fuel usage, and thus less revenue was raised from fuel taxes.
See also
- Fundamental diagram of traffic flowFundamental diagram of traffic flowThe fundamental diagram of traffic flow is a diagram that gives a relation between the traffic flux and the traffic density . A macroscopic traffic model involving traffic flux, traffic density and velocity forms the basis of the fundamental diagram...
- Road traffic control
- Traffic waveTraffic waveTraffic waves, also called stop waves or traffic shocks, are travelling disturbances in the distribution of cars on a highway. Traffic waves usually travel backwards in relation to the motion of the cars themselves, or "upstream". The waves can also travel downstream, however, more commonly become...
- Michigan LeftMichigan leftA Michigan left is an at-grade intersection design which replaces each left turn with a permutation of a U-turn and a right turn. The design was given the name due to its frequent use along Michigan roads and highways since the late 1960s. In other contexts, the intersection is called a median...
External links
- http://everything2.com/index.pl?node=green%20wave
- http://www.accesstoenergy.com/view/atearchive/s76a4022.htm
- http://www.onemotoring.com.sg/publish/onemotoring/en/on_the_roads/traffic_management/intelligent_transport_systems/glide.html
- http://www.bathnes.gov.uk/BathNES/transportandstreets/roadshighwaysandpavements/lightingtrafficlights/UrbanTrafficManagementControl/default.htm
- http://www.yairharel.com/2010/07/20/how-to-surf-the-green-wave
- http://www.sciencenews.org/view/generic/id/63481/title/To_tame_traffic,_go_with_the_flow
- http://www.sacs.dk/