Variable Speed Limits to Take Effect Sunday on Top Half of I-285

Beginning this coming Sunday (October 5), a system known as variable speed limits (VSL) will be in effect on the portion of Interstate Highway 285 north of its interchanges with Interstate Highway 20, the Georgia Department of Transportation announced today.

VSL will increase the base speed limit on this 36-mile section of I-285 to 65 miles per hour matching the limit on the southern half of I-285.  To increase safety and promote smooth traffic flow, however, Georgia DOT will be able to electronically reduce the speed limit on the top of I-285 in 10-mph increments to as low as 35 mph in the event of an incident or heavy congestion.

“VSL gives us the ability to warn drivers in advance that they are approaching heavy congestion or a crash site and to slow down that approaching traffic to a safe speed – one that will best facilitate its movement through the affected area,” GA DOT Chief Engineer Russell McMurry commented.  “This will be immeasurably safer than having to slam on the brakes when suddenly confronted with backed-up traffic.”

The success of the 65-mph speed limit on the south side and the abundance of I-285 lanes on the top – as many as seven and no less than four in either direction – validate the top side increase.  But there are distinctions between top and bottom.  The top half carries an average of 50,000 more vehicles a day – 100,000 more in certain locations, and there are nearly twice as many interchanges on the top.  More traffic and more interchanges equate to more merging and weaving movements, more congestion and more crashes – all of which can result in traffic backups. 

VSL will allow Georgia DOT Transportation Management Center operators, who constantly monitor I-285 via active traffic management software and closed circuit cameras, to instantaneously detect a crash, breakdown or congestion forming.   They then will be able to post warnings in advance of that area on overhead message boards and use 176 new electronic speed limit signs on the shoulder to make real-time adjustments to reduce the speed limit in and leading up to the area.  Speeds will be reduced in 10-mph increments as necessary to 55 mph, 45, and a minimum of 35 mph.

VSL has been successfully implemented in other states and research has shown that, in addition to increasing safety, it actually can help motorists arrive at their destinations faster – with VSL traffic flows in a more consistent, steady manner than via accordion-like “speed-up, stop; speed-up, stop” movements which also waste fuel and create more carbon emissions.