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Explaining how highway signs calculate if you're running late for work

The technology to calculate drive times is changing.

ATLANTA — Electronic signs along metro interstates help determine how long it will take you to get from one point to another, and the technology used to determine your drive time is getting more sophisticated.

Highway signs can warn you about nasty weather, alert you to construction in your path, and even peek into your future.

During the morning rush hour, we saw an electronic sign along Interstate 75 in Henry County claiming that a 5-mile drive to Hudson Bridge Road will take 5-7 minutes. The actual drive time was 4-minutes and 28-seconds. 

The signs change depending on traffic volume or wrecks that can impede your commute. They are Georgia Department of Transportation’s (GDOT) hi-tech way of letting you know if you’re running late.

Here’s how it works.

Metro Atlanta’s interstates are lined with cameras and radar. They measure how fast traffic is moving along different sections of interstate. A computer algorithm uses the data to calculate the drive time from point A to point B.

“We are always monitoring the system for anomalies to make sure that the algorithm is performing to our standards,” GDOT’s Natalie Dale said.

In areas that aren’t monitored by cameras or radar, GDOT depends on information provided by you. Apps on your cell phone ask you to share your location. It’s likely that your car has technology that tracks your movements through GPS and other means.

A third party collects the data emitting from your vehicle and provides it to GDOT to calculate highway speeds and drive time.

Dale says the data doesn’t identify who’s providing it.

“We would never know specifically whose phone that is,” Dale said. “We get that in a highly anonymous fashion. We would not be able to tell whose cell phone, what car.”

A wreck in the road ahead will quickly change travel times, which is why GDOT is constantly collecting information and updating the signs every 20 seconds.

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