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Posted: 7:35 p.m. Thursday, Sept. 20, 2012

Variable speed limit signs to go up on I-285

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285 photo
Phil Skinner, pskinner@ajc.com
Traffic backs up on I-285 near Ashford Dunwoody Road.

By Ariel Hart

The Atlanta Journal-Constitution

The legal speed limit on I-285 is set to rise to 65 mph - but cutting-edge traffic technology could lower it throughout the day.

The state Department of Transportation’s board voted Thursday to install electronic variable speed limit signs along the northern half of I-285. The speed limit will change depending on congestion, falling when the lanes get more full.

The idea is to make traffic move faster and more smoothly overall, by reducing the confusion and crashes from stop-and-go conditions — where drivers spot high-speed pockets and change lanes or shoot ahead briefly, then have to slam on their brakes.

“You’re able to move more traffic through” with the variable sign system, said Keith Golden, DOT commissioner. “If you’ll slow down you’ll actually get there faster,” Golden said, quoting traffic reporter Herb Emory of News Talk WSB radio.

DOT officials cautioned the speed limit is still 55 mph all the way around the Perimeter until the project is complete. It is just going out to bid now. As far as construction goes, it’s a relatively simple one that may just take a few months, possibly opening early next year, Golden said.

More than 260,000 vehicles drive I-285 each day, according to the Federal Highway Administration. If the system works, look for its expansion to other Atlanta highways such as the Downtown Connector.

Variable speed limit signs have been around for decades, for example to slow traffic ahead of a worksite or icy road. But DOT officials believe their system will be among the first permanent ones in the country for managing congestion. DOT will also use it to protect traffic from speeding into bad weather.

A similar system, installed to help safety on northbound I-5 in south Seattle, is working, Washington state officials believe. Another variant, in Australia, goes so far as to vary speed limits lane-by-lane, said Scott Belcher, president of the Intelligent Transportation Society of America.

The new system will only operate on the Perimeter’s northern half. On the southern half of I-285, where there is less traffic, no variable signs are being installed and the 65 mph speed limit will be standard. The dividing line will be about I-20, DOT officials said.

Some northern I-285 drivers were skeptical.

“How does taking down the speed limit to 10 mph if everyone’s going 10 mph keep somebody from jumping a lane,” said Danny Davis, a 36-year-old Lilburn resident who builds mobile apps. “It seems like it’s based on math and not reality,”

Moreover, he said, trying it out could cause more confusion than it solves. “Training someone for a new way of thinking when they drive is really difficult,” he said.

Golden said the changes would come in 5 mph increments and would not go “back and forth, back and forth.”

Ed Gueydan, 39, a general contractor who drives I-285 at least 10 times a week, agreed the congestion on I-285 is terrible, and it has caused him to change his work schedule simply to avoid it. But he thinks the new plan won’t work. “Nobody pays attention to the speed limit anyway,” he said.

Indeed, late Thursday morning, traffic on northern I-285 was a steady 70 mph, 15 mph above the current speed limit. Some vehicles were going about 80 mph, and the occasional one went slower on the far right.

“It’s just going to aggravate people,” Gueydan said. “I don’t see anything helping other than additional lanes.”

That’s the thing – additional lanes do alleviate congestion, but then they fill up again. And they’re enormously expensive compared to possible technological solutions like this one.

“I think it’s the future,” said Belcher, the ITSA president.

“From a traffic management standpoint it makes great sense,” Belcher said. “ If you’re all going at a constant speed, you’re going to go a lot quicker than that rush of exhilaration you feel when you spurt ahead only to get that crush of desperation when you’re now locked behind someone not going anywhere. It’s far better to go 45 mph constantly than stop and start to 65 mph.”

At least one I-285 driver – or rather, a Perimeter-area driver who avoids I-285 and its congestion “like the plague” – agreed.

“It sounds like a great idea,” said Chuck Cox, whose company develops technology to stop distracted driving. “Think about it, you’re managing the flow pressure.” There are hitches, he conceded – people don’t like to be controlled. “I think enforcement will be a challenge,” he added.

Enforcement is up to officers, DOT’s Golden said, but they are likely to be more concerned with aggressive driving or extreme speeding than with drivers who miss the lower limits by a couple miles per hour. “The intent of this is not to set a speed trap,” he said.

DOT’s traffic computers already monitor and count traffic congestion on Atlanta Interstates. On the I-285 system, a computer algorithm will suggest speed limit changes, and likely a person at DOT’s Transportation Management Center would approve each speed shift, Golden said.

“It’s awesome,” Belcher said. “There’s just not enough money to build the kind of infrastructure we used to build. So states, cities, and regions are going to have to look new ways to get as much as they can get out of the system they have.”

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