Solved? Where the “missing” Perimeter traffic went

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Has the traffic volume slightly decreased on some northern parts of I-285 over the past 20 years? Definitely maybe. (David Tulis / AJC file)

 

On Thursday, this blog reported that the number of vehicles using the northern part of the Perimeter actually declined over the past 20 years, according to traffic counts provided by GDOT.

Many of you balked. Typical reader comments: “Lies!” “This simply isn’t possible.” “Lunacy … What a crock!”

Bless your hearts. The numbers are real. But GDOT says you shouldn’t read too much into it.

First off, it’s generally the same volume of traffic, and this fact is more important to GDOT than a relatively small fluctuation in the data over the years. As GDOT spokesperson Annalysce Baker puts it, “Someone who’s 200 pounds, if they lose five pounds they’re still in the same weight class.”

If there’s truly a slight decrease, it could be due to a number of factors, according to Baker, including other routes getting improved and the tearing down of the GA 400 toll lanes. Drivers who may have driven across the whole northern part of I-285 may be peeling off sooner these days. Other factors could be in play too, such as gas prices and carpooling.

Sean Diehl, a GDOT data administration group leader, also cautions that the data collection is not meant to be definitive. Over the years, algorithms change, counting boxes get disrupted or damaged — it’s an imperfect science. “There are so many moving pieces that could have impacted the data collection at any given time,” he says.

So give or take 10,000 vehicles, there may be nothing to see here. Feel free to discuss it with your carpool buddies as you wait to exit onto Roswell Road.


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