Abu Dhabi improves traffic by adapting green lights
ABU DHABI // If you spend any time driving around Abu Dhabi you may have noticed that you're having better luck with green lights.
That's no accident.
Making the lights change to green as vehicles approach is one of the city's varied approaches to managing traffic signals, many of which have magnetic sensors embedded in the pavement nearby to count cars while a control centre monitors video of the rush-hour flow.
The city's transport plan has come a long way from the standard 30-second red lights that were in place at every junction a little more than a decade ago. Most lights are now timed and tailored to handle a certain volume of traffic at different periods throughout the day.
But the next step, one researcher says, would be to co-ordinate the customised junctions so that one can automatically react to congestion in other parts of the network.
Such a system could cut travel time by 10 to 20 per cent, according to Yaser Hawas, the director of the Roadway, Transportation and Traffic Safety Research Centre at UAE University in Al Ain.
"To optimise the system as a whole, you have to consider how what happens at one intersection will be felt at the next one a few hundred metres in each direction, and how those will affect the next ones, and so on," he said.
A similar network is in place in Dubai, and Dr Hawas is collaborating with Al Ain's traffic department to design a signal web, to be completed as early as next year.
While sophisticated analytical tools and simulation technologies are available to create something similar in Abu Dhabi, the city is not considering it, according to Ammar Kanaan, the intelligent-transportation systems specialist for the Department of Transport. That is because it could interfere with the predetermined timing needed for signal progression in place on many of the city's roads. Dividing the distance by the expected speed gives the driver a string of green lights, but at the expense of those waiting at junctions.
"Those who set the policy prefer the maximised volume and progression on the main roads such as Salam Street or Airport Road, but you could argue that even the side roads that are being penalised are also main roads," Mr Kanaan said.
"To maintain the green wave, it is very difficult to have optimal solutions for all intersections."
Mohammed Mostafa, a cab driver, said he has noticed traffic open up as he drives down Khaleej al Arabi Street. "When I am driving down that road, it is good," he said. "What I avoid is being stuck for a very long time on the sides."
Other lights in the city respond to demand, with set minimum and maximum spans for a green light. Seconds are added, up to a maximum, for each car that drives over the detectors. On roads less travelled, signals remain red until an oncoming car activates the green.
Adjustments to individual lights can also be made remotely from a control centre on Salam Street based on accidents, construction or anything else clogging the roadway. But the only way to completely limit the effects of a single incident is to have a sophisticated network in place, Dr Hawas said. Several times in the past couple of months, a bottleneck at one junction quickly spread to create hours of gridlock throughout the city.
"It's one thing to see an incident on a video screen and react to that, but if you don't have the real data or cannot adjust the entire overall network accordingly, you are only moving the congestion from one place to another place downstream," he said.
A good traffic engineer will know how to deflect traffic in certain areas by killing green time or making red lights irritatingly longer, Dr Hawas said. Sometimes it is even necessary to discourage people from driving altogether.
"Adding new infrastructure will relieve congestion temporarily, but eventually it will encourage more people to travel," he said. "If you go to downtown Al Ain you see people taking unnecessary trips to the store, kids hanging around in their cars, and you want to reduce these trips so the network is used more efficiently."
While engineers constantly take into account how the meticulously adjusted red seconds will annoy drivers, miscalculating yellow time can cause deadly accidents. The challenge is making the yellow long enough to eliminate risk but short enough that drivers will respect it.
"In our minds, we might know how long we expect the yellow light to be and believe we'll get through the yellow with enough time," he said. "The fractions of seconds, the difference between 3 seconds and 3.5 seconds, could create an opportunity for accidents to happen."
Most intersections in Abu Dhabi are set at four seconds, including a second that the red lights overlap, Mr Kanaan said. Yellow lights at a couple of dangerous intersections are a second or two longer.
For Dr Hawas' ideal network, no system would be uniform.
"We are able to do the research to find out about drivers' behaviour and adjust each light according to society, even the yellow lights," he said.
Updated: October 24, 2010 04:00 AM