I-Team: Are yellow lights too short when making turns?

The ABC11 I-Team uncovered a problem with the formula that the DOT uses to set the length of yellow lights.
May 6, 2014 12:21:21 PM PDT
If you've ever gone through a yellow light just as it was turning red, and thought it was quick, you might be right.

The ABC11 I-Team uncovered a problem with the formula that the North Carolina Department of Transportation uses to set the length of yellow lights.

It happens every day. The green light turns yellow, and you have two choices. You can hit the brakes, or try to beat the red light.

As it turns out, you have a much better chance of making it if you're going straight. In fact, if you're turning, the lights are in a way rigged against you.

"This is a safety problem," said driver Brian Ceccarelli.

Ceccarelli first took notice back in 2009 when he tried to make a yellow, but wound up running a red light.

"When I saw the camera flash, I knew there was something wrong," said Ceccarelli. "There was no way I could stop at this light in time."

Ceccarelli became a man on a mission. He started the website redlightrobber.com, and used his background as a physicist to figure out why yellow lights seem so short.

"The formula actually violates the laws of physics for certain types of motions, traffic motions," said Ceccarelli.

Ceccarelli said the Department of Transportation's formula for yellow lights only works for cars going straight through the light, and only cars that stay at or above the speed limit.

"It doesn't apply to any type of traffic movement that has to decelerate into the intersection," said Ceccarelli.

To check Ceccarelli's math, the I-Team went to the source. Alexei Maradudin is now a physics professor at the University of California - Irvine. In 1960, he came up with the root formula, which is still used by the DOT.

"That's correct. We did not, in our analysis consider turns; either left and turns or right hand turns," said Maradudin. "It was really straight through the intersection dynamics that we considered."

That formula made it into the traffic engineering handbook, and has been used, or misused, as Ceccarelli puts it in North Carolina, and across the country ever since.

"It causes lots and lots of people to run red lights, involuntarily," he said.

According to Ceccarelli, yellow lights should generally be three to four seconds longer. So, why are they set as they are? Based on a flawed formula written 55 years ago?

"I think that's a question that should be addressed to the Departments of Transportation," said Ceccarelli.

MORE INFORMATION

The DOT provided the following response to our I-Team story on the length of yellow lights: Click here to read it.

LINKS

The NCDOT yellow light change interval spec: http://redlightrobber.com/red/links_pdf/NCDOT-Yellow-Change-Interval-Spec-Sheet.jpg

Which you can find as equation 9 on page 118 in Maradudin's 1959 paper: http://redlightrobber.com/red/links_pdf/The-Problem-of-the-Amber-Signal-Light-in-Traffic-Flow.pdf

A Letter Maradudin sent to the California DOT: http://redlightrobber.com/red/links_pdf/Yellow-Change-Interval-Dos-and-Donts-Alexei-Maradudin.pdf


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