Dr. Traffic

We all pay a price when you put on makeup instead of driving

A worker prepares to bury a sensor in the pavement.
A worker prepares to bury a sensor in the pavement. Charlotte Department of Transportation

Time management strategies can serve us well, but not in traffic.

When you’re sitting in a left turn lane, for example, do you look for ways to be productive while you wait?

Maybe you flip through your radio stations or playlists, check your hair and makeup, or scroll through emails? (That last one could get you a traffic citation, by the way.)

If your multitasking distracts you for two to four seconds or more, you could cause a ripple. That’s sci-fi talk for altering the course of the future.

In this case, you alter the flow of traffic – perhaps more than you would imagine.

That tradeoff between personal productivity and less efficient travel for everyone else in your immediate traffic stream doesn’t sit well with Jim Sisco of Mooresville.

“My guess is that 10 percent more cars could pass an intersection in a day if everyone understood this and paid attention,” Sisco said.

To understand how Sisco arrived at his conclusion, it helps to know more about the workings of Charlotte’s 755 traffic signals. I got help with that from Charles Abel, transportation systems manager for Charlotte Department of Transportation.

Charlotte has two types of signals, Abel explained.

In uptown, most signals operate on timers without regard for the number of cars on the streets, Abel said. This system gives uptown’s high volume of pedestrians time to cross the intersections.

Outside of uptown, many signals have vehicle detection technology in addition to timers. That means the lights in some lanes stay green for a time as long as sensors in the pavement detect vehicles, Abel said.

The idea here is to keep traffic moving on major streets. Sometimes that means shortening green lights on side streets when there’s no traffic waiting, Abel said.

The sensors for left turn lanes are especially sensitive, for instance. If a vehicle doesn’t move with everyone else when the light turns green, creating a gap in traffic flow, the green light will likely go away. That means fewer cars will get through an intersection, and the line will be longer for the next cycle.

“For a congested intersection, that can mean many cars did not get through,” Abel said. “They aren’t getting time we could have given if we were running more efficiently.”

Here’s the telling part: The detection time before a signal change was about two to three seconds seven or eight years ago. We’re so distracted that traffic engineers increased it to two to four seconds, to answer complaints about long lines at some signals.

We can do better.

For starters, don’t be offended the next time you’re distracted and someone blows a horn to get you focused on the road again. In this case, it seems the best way for a driver to be productive is to do one thing at a time.

Karen Sullivan: drtraffic@charlotteobserver.com, @Sullivan_kms

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