Atlanta, Georgia's 'Top End' Gets Variable Speed Limits This September

June 23, 2014

Computers have brought us many great things. Online shopping. Streaming movies. Minecraft. And, lest we forget, variable speed limits.

If you're not familiar with variable speed limits, they're exactly what you'd think: traffic systems designed to change speed limits in a given area, based on weather, traffic, and other factors. Variable speed limits have been used in parts of the U.S. for over 50 years, with Michigan rolling out one of the country's first programs in 1962 (PDF).

However, variable speed limit systems don't always rely on advanced technology. For example, some are designed to change speeds during particular times of year. That's how it works on an interstate in Wyoming, where top speeds are reduced during snowy, icy winter months. The Cowboy State's system wasn't meant to be responsive to minute-by-minute conditions; limits change based simply on the day of the year.

But of course, other systems now deploy an array of sensors to assess weather, traffic, and other factors when changing speed limits. That's the kind of system that's headed to Atlanta, Georgia -- arguably, one of the most congested cities in the country.

According to the Georgia Department of Transportation website, I-285 is a trouble spot -- specifically a 36-mile stretch of it, located to the north of the I-20 interchanges. This section, called the "Top End", is where variable speed limits will be introduced this September. The DOT says that it hopes the system will make I-285 safer and less congested.

The DOT says that it'll accomplish that task by keeping traffic moving at the same speed. While speeding itself can cause accidents, a major cause of collisions is "speed variance", or travelers moving at vastly different velocities. The new system in Atlanta aims to mitigate the possibility for differences by ratcheting down (or up) the speed limit from a maximum of 65 mph down to 35 mph, using a network of 176 digital signs. Though traveling down an interstate at 35 mph is no one's idea of fun, the DOT says that it's safer and more efficient for drivers to slow and move at the same pace than to keep a higher speed limit, which encourages stop-and-go traffic. 

And for those who think that police are always looking for ways to write more traffic tickets (not a stretch, since many cities depend on revenue from citations), Georgia's DOT states very clearly, "Our ability to remotely change the speed limit on the corridor is not intended to create speed traps. Rather, the changing speed limits are designed to create safer travel by preventing accidents and stop-and-go conditions."

Georgia officials say that the new system is inexpensive and easy to roll out, with a strong return on investment. They hope to see results similar to those of a variable speed limit system deployed in Washington state, which curbed collisions by 13 percent and injuries from collisions by 10 percent.


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