Green wave

In a green wave the traffic lights of a road train are switched so that you can at a certain speed encounters each traffic light in their green phase when driving on the road. This velocity ( rate of progression ) is indicated in some cases, additional tables, such as Green wave at 40 km / h The advantage is a more continuous traffic flow of vehicles.

It is noted, however, that this system can be applied only in one direction, while the other must stop by more frequently ( often colloquially accordingly called Red Wave ). For this reason, this light circuit is often used where one influence certain traffic flows, or would prefer (eg for vehicles at peak times quickly out of the city, or in the opposite back to the city to lead into it ). Only in rare cases, the Green Wave can be applied in both directions. Further details will be explained below.

Planning

The control method of the green wave is an example of valid in Germany guidelines for traffic signal (short RiLSA ) explained here. There, when planning a green wave a number of parameters must be considered:

In practice, the wave is usually at critical intersections between two main streets, " hung up " and developed from there in both directions. Depending on the distance between the cross streets is often only a directional coordination possible. According to the load of the traffic into town or out of town coordinated. The respective opposite direction must stop frequently.

By Pulkbildung it comes to more uniform traffic. However, usually decreases the performance of the traffic light systems involved, since the receipt of the green wave periods are to be connected, which would actually ask for the cross traffic. From a utilization rate over 80-85% of the breaking wave by vehicles that must stop at Pulkende of Red, together. In really dirty streets must therefore be abandoned during rush hour traffic in favor of a maximized performance, the green waves.

A green wave in both directions is possible only if the distance of the light signal installations corresponds to the part point distance or a multiple thereof. With an orbital period of 90 seconds and a maximum speed limit of 50 km / h, 625 m, at 70 seconds and 50 km / h, 486 m.

Coordination systems

In the coordination of multiple nodes, there are two basic methods. We distinguish between the simultaneous system and the alternative system.

The simultaneous system is all crossings of a green belt free time. Thus, the node distance can be calculated as follows:

In the alternative system, the node sharing is shifted by a half turn. The Knotenpunktsabstandsberechung is then:

Variable assignment:

Expiration

A green wave is not a wave in the physical sense. Nevertheless, it has in common with physical waves some properties. Therefore, the following presentation serves as an illustrative model, less as an explanation for the green wave.

There is such a thing as oscillators ( the traffic lights ) that run something like vibrate and thereby periodically the same traffic light phases through ( red, red - yellow, green, yellow, red, ...). There is the oscillation period T, the period between (for example ) red stage and the next. There is a frequency f which is the frequency of the phase change. And it is true:

For example, if red is repeated every two minutes (T = 2 min), then the frequency f = 1/2 cycle per minute.

If you look along the stretch of road, we see the same phase traffic lights at certain intervals. This distance has the character of a wavelength λ.

The " spread" of the wave we follow best by following the chronology of the meetings of a vehicle with the individual lights. It "rides " on the shaft by hitting every traffic light in green, So along the road moved at the same speed as the wave. The following sequence shows the condition of the road at time intervals T / 4

Between the first picture (at time t = 0) and the last picture ( at time t = T), the carriage moves to a wavelength, the phases of all the traffic lights along the road are the same in both images; the shaft is moved by one wavelength and each traffic light once all phases through ( each oscillator performs a full oscillation ). The speed of the vehicle ( and thus also the propagation velocity c of the shaft) is the distance (ie, λ ) divided by the time required (ie, T). Therefore applies

In addition, since f = 1 / T ( see above), also applies

For example, if T = 2 min and λ = 1200 m ( distance a green light from the next ), then c = 1200 * 1 / (2 min) = 600 m / min ( = 10 m / s = 36 km / h): Green wave at 36 km / h

Interference

Several factors can interfere with the homogeneous traffic flow in a green wave:

• Switched depending on traffic light systems (LSA ) because of the varying green times, especially disturbing acceleration circuits of public transport can act
• Crossings
• Circumcision of the green time for the shaft because of changing number of phases (eg due to separate the signaling traffic turning left )
• Driving at speeds above the rate of progression (often through inattention or lack of information on the rate of progression )
• Dissolving the vehicle groups with very large LSA intervals (approximately 750 m)
• Barriers to the flow of traffic by parking in the second row ( delivery traffic, taxis ... )
• Change of the road cross section (eg, expansion of a same direction on two lanes, and vice versa )
• Successive LSA with different phase sequences, for example separately signaled Linksabbiegeverkehre

History

The first, manually coordinated circuit of traffic lights at six intersections was introduced in 1917 in Salt Lake City. From 1926 there was a manually controlled green wave in the Leipziger Straße in Berlin. In the 1970s, the green wave and an additional traffic light display was introduced, which stated that speed is just necessary so that the passing car may comply with the shaft optimal ( speed signal). The display had three fields at 40 km / h and 50 km / h and 60 km / h ( or different), one of which glowed white. The success, however, remained in most cities and such additional ads were (except for some ads, for example, in Dusseldorf, Suhl or in Wiesbaden) removed.

In the GDR special number advertisements existed behind the crossings, which usually specified in increments of five, the recommended speed to reach the next traffic light green means go. This also allowed the oncoming cross traffic, in the green wave " einzutakten " and so to reduce the waiting time at intersections. Since these displays are not provided in the Federal German Road Traffic Regulations, but they were shut down after the turn and now dismantled for the most part.

Traffic signals for cyclists are coordinated in a green wave in Copenhagen as part of bicycle paths Quick first time.

To improve performance, traffic signals are switched increasingly depending on traffic - thus the varying green times make the speed recommendation virtually impossible.

Green Wave works in both directions only when longer green phases or low signal conditioning density. This is achieved in the U.S. through Allowed turning right on red and on-demand turning left lanes. In this respect the left-bending the right of way to oncoming traffic and get only needed a period of LSA connected explicitly.

Norms and Standards

• Guidelines for traffic lights ( RiLSA )

• RVS 05:04:30 ff - Traffic light systems ( VLSA )

• SN 640 840 - light systems; Coordination in road trains using the method of partial credit reserves