Intelligent intersection control

Intelligent intersection control systems have a growing role to play in making urban traffic more efficient. Robin Meczes reports.

The idea of every traffic light turning green as you approach it has long been a dream for many an urban driver – and none more so than those driving heavy goods vehicles (HGVs), which are slow and difficult to bring to a halt and then accelerate back to normal travel speed. But that dream has become a reality for some drivers in a small number of cities around Europe in the last few years, thanks to the 372 Freilot project, and now looks set to do the same for many more with the launch in January of the 7288 Compass4D pilot in several other locations.

The EU co-funded Freilot (Urban Freight Energy Efficiency Pilot) scheme was a cooperative mobility services project that began in October 2010 and tested a range of intelligent systems including energy-efficient intersection control, eco-driving support, loading bay advance booking, and in-vehicle speed and acceleration limiters, all designed to help boost safety and efficiency while reducing fuel consumption and vehicle emissions. The pilot was conducted in four European cities – Helmond (The Netherlands), Bilbao (Spain), Lyon (France) and Krakow (Poland).

The trial was a striking success – particularly in terms of energy-efficient intersection control. Ensuring that emergency vehicles and heavy trucks could pass through junctions more often on a green light boosted travel times and cut fuel consumption, as well as reducing the kind of collisions that so often occur at intersections.

In Helmond (The Netherlands), site of the most prolific energy-efficient intersection installation in the scheme, the project resulted in test vehicles being stopped at traffic light controlled intersections just 6% of the time, rather than 13% before. That contributed to a 13% reduction in fuel consumption and a 2.6% increase in the average speed of HGVs through the test routes. Fire engines, meanwhile, which were given even greater priority, enjoyed an even bigger speed improvement of 8%.

Though the trial has now come to an end, the system in use in Helmond continues to operate. Covering 13 separate intersections, it uses on-board units (OBUs) in vehicles that communicate with the intersection’s Road Side Units (RSUs) using the 802.11p protocol – a wi-fi variant optimised for communications between moving objects. Approaching vehicles and RSU become aware of one another about 800 metres in advance of the intersection, at which point the RSU decides what priority is appropriate. For emergency vehicles in full flight, lights would be turned green; for trucks, lights would be turned green where practical or, as a minimum, advice would be issued by the RSU to the in-cab screen about what speed to adopt in order to reach the light as it turned green.

Siebe Turksma, product manager, research at 769 Imtech (formerly Peek Traffic), which supplied most of the Freilot RSUs, as well as the OBUs and associated software, says the net result for HGVs was a much greater probability of passing through lights without stopping. He admits, however, that prioritising some vehicles in this way can disadvantage other traffic. “The fire brigade gets a very hard, absolute form of priority – that can be very disruptive for other traffic,” he says. “In busy times, you have to allow about 10 minutes before things return to normal – though obviously, in quieter times, the disruption is not so great.

“For HGVs, the priority was far lower,” he continues. “It was a case of increasing the probability of them getting a green light.

Where they might normally have a 20% probability of not having to stop, they would perhaps have a 40-50% probability of that with the system in place, depending on the intersection.”

The degree to which other traffic is disrupted depends largely on traffic density in general and on how many priority vehicles happen to be in the area at any given time, he admits, but local traffic authorities can easily mitigate the effects by reducing priority for HGVs during the rush hour to compensate. “As long as you have a normal penetration of HGVs in a normal urban environment and you’re not close to saturation, we found the average situation improves,” he comments.
Besides, in many ways, other vehicles also benefit when HGVs are kept moving. “What often happens at an intersection is that an HGV is the first vehicle to stop, because there is often a gap in front of it due to its poor acceleration. That not only means there may be a lot of vehicles behind it that also have to stop, but also that it’s the first to get moving again, and because of its slow acceleration it holds other vehicles up again. That’s two inefficiencies you get – so giving HGVs a bit of priority also benefits other traffic.”

Next steps

Energy-efficient intersection control of a similar kind is now to be employed in Compass4D, a new EU co-funded three-year project that was launched in January and will see deployment of the technology at locations in seven European cities: they include an extension of the Helmond system to nearby Eindhoven, as well as fresh sites in Bordeaux (France), Copenhagen (Denmark), Newcastle (UK), Thessaloniki (Greece), Verona (Italy) and Vigo (Spain). It’s not yet determined which suppliers will provide the system, but the intersection control will again be via RSU and OBU and is likely to provide similar benefits in term of carbon emissions and fuel consumption, suggests Turksma.

The Compass4D project will, however, be more broadly targeted, taking in private cars, taxis, buses, emergency vehicles and freight vehicles – over 330 vehicles in all. It will also test two other types of safety system using RSU to OBU communications: red light violation warning, which will alert both the driver of a vehicle that looks likely to violate a red light and other drivers in the area of the impending risk, both via the OBU screen and with an audible alert; and forward collision warning, which will forewarn drivers of congestion or queuing ahead as a result of traffic volumes, road works or an accident.

The first functioning sites should be up and running early next year, says Pierpaolo Tona, project manager at 374 Ertico-ITS Europe, which is coordinating the whole Compass4D project.

“There is a lot of enthusiasm in the consortium” he says. “We will start installation of RSUs and OBUs early next year. Then there will be a three-month period of baseline measuring, before we move to full operation with all the vehicles. All of the trials should be ready by mid-2014.”

All three safety systems – red light violation warning, forward collision warning and energy-efficient intersection control – will be implemented in all seven cities. In one case – Bordeaux – RSUs will not just be deployed at intersections but also on three dangerous curves on the city’s ring road.

Tona confirms that in terms of fuel and carbon emissions, similar results are expected to those of Freilot. What’s less clear, he says, is what accident reduction might occur, since establishing a reliable baseline is very difficult. “We have some estimates on energy consumption, based on the results of Freilot. On safety, however, we can’t really be as precise as historical data are not really identifiable by particular intersection. It’s something we’ll be looking into in more detail as the project progresses,” he says.

As with Freilot, large vehicles will be given priority at intersections to help get them out of the way as soon as possible. Although they don’t get any priority at intersections, meanwhile, the inclusion of cars and taxis in the Compass4D project will still smooth their passage through junctions too. “Even vehicles which aren’t granted priority, can be given speed data to help smooth their approach and ensure they pass the light on green,” Tona points out.

Seeking standards

It remains to be seen just what the specification will be for RSUs in the Compass4D project, but the plan, says Tona, is to advance global standards in such systems. Transport experts from both Japan and the US are involved via secondment agreements with the European Commission and Compass4D will build on this tri-lateral cooperation. Soon, representatives of the Compass4D project will be visiting the Ann Arbor Safety Pilot in Michigan to evaluate their work, he reveals.

“The target is to have a single specification or, if not, to at least make sure that systems of different RSUs and OBUs will communicate with each other. We don’t want different parts of the world using three different RSUs,” he comments.