Wai Cheung is about to try the seemingly impossible, get drivers on the Whitemud Freeway to move faster – by slowing down.
Wai’s a technical specialist with the City of Edmonton’s Transportation Services department, and part of his scope is what’s called ITS – intelligent transportation systems.
Sitting on the 16th floor of Century Place in what he calls his ‘cave’, Wai explains a pilot project the City is about to engage in with the University of Alberta’s transportation engineering department.
“During periods of high congestion, we’ll be trying to avoid the ‘shock waves’ that travel backward from vehicles that need to slow down drastically to make space for other vehicles merging from entry ramps.
“When it’s congested, those shock waves travel backward a very long way, slowing hundreds of vehicles down because of an event that may have occurred several minutes ago,” he says.
“And the very worst shock waves are when people actually stop on the freeway. Once they start moving again, every vehicle behind them will also have to stop – all through the congested period.”
The City has installed vehicle detection systems (wire loops buried in the pavement that detect passing vehicles and their speed) every kilometer on the Whitemud between 122 Street and 170 Street, and on westbound entry ramps in the pilot program zone between 122 Street and 156 Streets.
“Those systems tell us in real time what the traffic volume is both on the freeway and the ramps, so at any point in time our computers can calculate the optimum speed for people to drive in order to smooth traffic flow and keep traffic moving,” says Wai.
“We’ll then wirelessly forward that optimal speed – what we call the advisory driving speed – to standard orange roadside traffic advisory signs beside the freeway.”
If people heed the variable advisory speed, which will change with traffic congestion in increments of 10 kilometers per hour, the maximum number of vehicles will be able to move on the freeway with the least amount of delay.
“They may have to slow down, but if they follow the speed advisories, they’ll get where they’re going more quickly than by trying to go faster,” he says.
Wai says the City’s grateful for its partnership with the U of A, particularly Dr. Tony Qiu.
“Their graduate students started with our base model and the information we had on the Whitemud Freeway’s traffic flow patterns, and fine tuned the model to a very much greater extent.
“The combination of their work and our data-gathering infrastructure will enable this pilot to happen,” says Wai.
The pilot is scheduled to start August 11, and to last for a month.
“We’ll then analyze the results and make further decisions from there,” says Wai.
“If we’ve been able to reduce collisions and maximize throughput on the Freeway, we’ll consider it a success.”
Other world cities use the same principle, and some are very forceful about it. London, for example, displays variable speed limits for every lane of congested roadways, and uses photo radar enforcement to ticket drivers who try to go faster than the variable limit.