For the first time, variable speed limits seem headed to a metro Atlanta interstate, in a plan under way at the state Department of Transportation. And they would often allow speedier traffic on I-285.
DOT has a plan -- not now, but sometime within the year -- to raise the speed limit on I-285 to 65 mph from its current limit of 55 mph, according to DOT spokesman David Spear. It is unclear how much of I-285 would be changed by the plan.
At the same time, the department would for the first time install permanent electronic speed limit signs on a Georgia interstate highway, Spear said. They would allow DOT to lower the speed limit in case conditions warrant, for example in case of bad weather or an accident ahead.
“As I understand it, the principle is harmonic balance, whereby if we can get motorists in a congested segment to all slow down, the traffic actually flows better,” Spear wrote in an email.
The plan has not yet been presented to the DOT board, Spear said, and staff would likely seek the board's concurrence before proceeding. Board Chairman Rudy Bowen said he would need to see the reasoning and data before deciding. Spear did not know when it would be presented to the DOT board.
Speed limits that are not set in stone are nothing new. Metro Atlanta drivers are familiar with limits that change during school hours, or when roadwork is under way.
But these signs could be more consistently changed.
A study for the Wyoming Department of Transportation surveyed variable speed limits implemented elsewhere in the U.S., and found that “overall each DOT believes that the system is working on their corridors.” It found that one system in Virginia is automated, but the other 10 states’ systems required approval before changing the posted speed.
A spokeswoman for the Georgia Governor’s Office of Highway Safety did not respond to a call. The previous director of the office, Bob Dallas, said a proposal to raise the speed limit concerned him. Encouraging higher speeds could lead to more severe crashes, he said. Not only is that bad in itself, but such crashes take longer to clear from the highway and cause more congestion, he said.
After Wyoming implemented variable speed limit signs on parts of I-80 in 2009, preliminary safety results were encouraging.
Wyoming's study said it needed more years of data to draw reliable conclusions, but that crashes overall had decreased. The level of fatal crashes didn't change much.
Pat Persson, district engineer where the variable speed limits are on I-80, said that winters had been so different it was tricky to say what caused the changes. However, "The overall feeling of the patrol and the maintenance people that work out there is that motorists are behaving better and we’re getting people to slow down in a group, that’s the important part."
As for the public's reaction, "We’ve had a couple of them [the signs] shot up," he noted, but in general, "the public, who I talk to frequently, is very positive about these variable speed limits. They like to see the lower speed limits lowered to the weather conditions."