Ask for well-adjusted traffic lights, a so-called 'green wave'
You tackle the following challenges:
That's how you do it
Coordination of traffic lights appears to be an effective means of limiting travel time and noise pollution. It improves traffic flow and probably also reduces pollutant emissions. Changes in the traffic flow sometimes affect travel time, noise pollution and air quality in a different way. For example, a smoother traffic flow will lead to lower emissions, but not necessarily to less noise pollution. In general, traffic light coordination is seen as a valuable tool to improve urban air quality, although there is unfortunately little scientific data to support this.
The coordination of traffic lights is often seen in cities with an environmental zone and the system plays an important role in controlling traffic flows. Below we give some examples of statically and dynamically controlled systems (also in combination with public transport).
In general, the coordination of traffic lights has a beneficial effect on traffic congestion and air quality. The impact on emissions is mainly related to the so-called 'green time', which varies according to traffic demand. Unfortunately, not many studies are available to substantiate the effects on air quality.
- Particulate matter (PM) : The effect on PM 10 turned out to be negligible according to a Dutch study. Both with and without green wave, the model estimates the traffic contribution of PM 10 to be about 2 to 3 µg/m³.
- Nitrogen dioxide (NO 2 ) : in the same study, the modeled traffic contribution to NO 2 on certain stretches of the road was 8 to 10 µg/m³ where there was no green wave, versus 6 to 7 µg/m³ with a green wave. A Belgian study concluded that the introduction of a green wave could potentially reduce emissions by 10 to 40% under the most favorable conditions.
- Soot (EC) : no information available.
Entering a green wave offers other advantages :
- Road safety is increasing
- Transport is faster, and therefore more efficient from an economic point of view
- Better accessibility with different means of transport
- There is less noise nuisance at the traffic lights, but more between the intersections.
- Vehicles consume less fuel
- Cars wait less long on the side roads
- Pedestrians have more time to cross at intersections
Knowing more
Model study on statically controlled systems
Antwerp, Belgium - 2011
In an Antwerp residential zone, a model estimated the effects that speed limits and traffic light coordination have on CO 2 and NO x emissions. According to the calculations, emissions would decrease by 10% if the traffic lights on an urban artery function in a 'green wave'. The effect of the speed limit was approximately 25%.
Model study on dynamically controlled systems
Ghent, Belgium - 2012
A model study in Ghent shows that the traffic intensity and the duration of the green phase (this is the variable green time depending on traffic demand) have the greatest influence on air-polluting emissions. The cycle time of the traffic lights had little impact. Under the most favorable conditions, a green wave can reduce emissions by as much as 40%, this study showed.
Traffic light coordination
London, UK - 2000
To study the potential benefits for air quality when traffic congestion and congestion were reduced, London's traffic lights were linked to the urban traffic control system. The SCOOT system (Split-Cycle Off-set Optimization Technique) was used for this. SCOOT initially worked at about 3,000 of the 6,000 intersections.
In 2009 and 2010, Transport for London revised the timing of traffic lights, reducing start-stop wait times at traffic lights by approximately 6%. SCOOT has since been introduced at 1,500 additional locations to further reduce waiting times and reduce congestion.
Model study on traffic light coordination
Leiden, Netherlands - 2006
A model study was conducted in Leiden into the effects of a green wave based on the Dutch CAR model. A 35% reduction in emissions thanks to the green wave was assumed. The contribution of traffic to NO2 concentrations decreased from 8 to 6 µg/m³.
Replace traffic lights with roundabouts
New York, USA - 2006
Replacing a traffic light intersection with a roundabout is another way to influence traffic flow. This pilot study showed that such a measure could reduce NO x and CO 2 concentrations by 16 to 21% compared to traffic lights. This also improved the traffic flow.
More information
- Madireddy et al (2011) is an interesting study that provides an example of a coordinated approach to heavy traffic and vehicle emissions. The authors estimate the impact of speed limiting and traffic light coordination on vehicle emissions through modelling.
- Better mobility in Copenhagen , ITS Action Plan 2015-2016 gives good examples of different pilot studies on the implementation of traffic light coordination in the city of Copenhagen (November 2014).
- The strategy designed by the London authorities was presented in: Roadmap of transport emissions, cleaner transport for a cleaner London (September 2014), including the implementation of a traffic light coordination system.
