The speed limit on I-285 has long been considered optional for many Atlanta drivers. Lately, though, it’s just plain unreliable.
Technical glitches have been plaguing the variable speed-limit signs along the top end of I-285 almost since the time the $4.9 million system was installed in October 2014.
Should you go 35 or 55? Drivers could encounter signs displaying both speeds. And we’re not talking about signs miles apart, but those posted directly opposite each other on the median and shoulder.
In July and August, on average more than 20 percent of the 176 signs were wrong at any given time. As of Monday, 12 of 176 signs were malfunctioning; four signs were out of commission because motorists had mowed them down; and 10 were switched off because they were near construction zones.
Mixed messages are happening because signs posted on opposite sides of the road often have problems “talking” to each other via wireless radio signals.
That is, if the signs are displaying numbers at all.
“We have not been real satisfied with the performance of the technology,” said Commissioner Russell McMurry of the Georgia Department of Transportation. “I think we’re going to work our way through it.”
It all adds up to one pretty confusing ride, said Chris Dalbec, a Sandy Springs resident who travels the top-end Perimeter on his weekday commute from Peachtree Industrial Boulevard to Camp Creek Parkway.
Dalbec said he saw one sign that had the digits reversed, so that it displayed 56 (instead of 65). He’s also seen a sign that was just blinking “6.”
“It makes me really hesitant to believe really any of the signs, until I see two in a row that are the same speed,” Dalbec said.
The purpose of variable speed limits is to alert drivers that traffic congestion is imminent. Sensors on the interstate detect traffic jams and automatically reduce the speed behind the jam, which is supposed to result in a smoother traffic flow instead of the maddening stop-and-go.
On the top end of I-285, the system works by decreasing or increasing the speed limit by 10 mph increments between 35 and 65 mph.
The variable speed limit system is only in place from I-20 East to I-20 West. On the lower half of the Perimeter, the speed limit is consistently 65 mph.
The top side carries an average of 50,000 more vehicles a day than the lower half of the Perimeter, and has nearly twice as many interchanges. That means drivers are doing more merging and weaving, which means more congestion, crashes and sudden slowdowns.
Sandy Springs Police Department has jurisdiction over about five miles of the top-end Perimeter. Department spokeswoman Sgt. Forrest Bohannon said the sign malfunctions have not caused any uptick in wrecks.
“I’ve asked around and nobody has any specific incidents of those variable speed-limit signs causing any accidents,” Bohannon said.
However, state transportation officials acknowledge that the glitches are causing drivers like Dalbec to distrust the information on the signs.
“The whole idea is to alert the driving public that there is something going on, but it’s the boy who cried wolf syndrome,” said Dalbec. “It says you need to slow down. And then you get there, and there’s nothing there.”
Transportation engineers plan to tweak the algorithm that tells the signs how far in advance of congestion they should reduce traffic speeds. More drivers will heed the slowdown warnings when they start to see the correlating traffic jam up ahead, McMurry said.
GDOT expects that a firmware upgrade scheduled for early 2016 will fix many of the remaining problems with the signs’ wireless communication systems.
Either way, the variable speed limit signs are here to stay.
“We very much believe in the technology,” McMurry said. “If we continue to have issues, then we’ll just have to deploy another technology. The concept of notifying people that something has changed ahead and they need to slow down is so important.”
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