Carl F. Thelin

YELLOW LIGHTS

A newspaper story asked some questions:

City Lengthens Yellow Light Time For Safety

20 Targeted Intersections See Yellow Longer

POSTED: 9:04 am MST January 19, 2011

ALBUQUERQUE, N.M. -- The city of Albuquerque will extend the length of yellow lights at 20 current and past red-light camera intersections across the city in an attempt to make those areas safer.

It will cost taxpayers $3,600 to change lights at intersections, but city leaders said they're investing in safety.

"We are looking at everything to improve the public safety at these intersections besides the red-light camera," city spokesman T.J. Wilham said.

Many yellow lights will now stay yellow for 1/2 second longer. City leaders said that two national studies show it will deter drivers from running red lights and prevent crashes.

"(One study showed) increasing the length of a yellow light from half a second to one and a half seconds had reduced crashes by 50 percent," Wilham said.

In addition to increasing yellow light times, the city also increased the times when all four lights are red.

"That gives anyone who might be running the red light time to clear that intersection before someone could be coming the opposite direction," Wilham said.

City leaders said a University of New Mexico study showed that certain red-light cameras help keep drivers safer.

"But it also told us, by making other adjustments such as increasing the time of yellow lights or increasing the time all lights stay red, also increases public safety," Wilham said.

The city also hopes to get the green light to look at adding better signage and to improve rumble strips in the near future.

If these improvements work at the 20 targeted intersections, then city leaders said they could expand the procedures.

The changes went into effect in early January.

Copyright 2011 by KOAT.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

=======  here is what I have to say: ========

AMBER-LIGHT ARITHMETIC

              How long should a yellow signal be? That issue has filled up several columns of the local newspaper’s letters to the editor. One writer wanted the amber light to last longer. Another said red-light runners were good people who didn’t mean to blow through the signal. I assisted the columnist with this reply:

            I said, “Baloney - you can try to reduce the danger of running red lights but none will protect you from a determined, risk-taking scofflaw. Break it down this way:

  •     You need to know that the traffic signal is there. Don’t tailgate a high profile SUV or truck that blocks your view of the signal — the brake lights on that vehicle are no substitute for what’s going to happen with the traffic signals.

• You need to decide what to do. This might take anywhere from 0.5 to over 3 seconds. If you are all keyed up, with your right foot poised to press on the brake pedal, make that a half second to decide to push down on the pedal. If you are daydreaming, not paying attention, a longer time number applies. Let us use a number like 1 second, here.

  • You need to do something. It takes time for a driver to lift his foot from the accelerator and place it on the brake pedal. It also takes a small bit of time for the pedal to go down and for the hydraulic fluids to push the brake elements into action. For example, assuming you are quick, let’s use 0.5 second for the foot to push down when it is ready. That means it takes 1.5 seconds before stopping actually begins.

   • You expect to stop quickly. This time frame is dependent on how hard you brake — slam your foot down – assume 0.8 g braking - your passengers will complain, and you might even scare the daylights out of the driver behind you. You will slow from 45 to 0 mph in about 3 seconds in less than 100 feet. That is panic braking and not a nice way to drive.

            Braking from 45 mph with at 0.1 g means you have to keep an eye out ahead, plan to use about 700 feet and take about 20 seconds to stop. It is reasonable to double the deceleration rate; come to a stop in 350 feet in half that time. Put it all together and a driver traveling 45 mph will take 1.5 seconds to react and begin braking. At 45 mph, you travel 66 feet per second; you cover 100 feet just to begin slowing.  Add 350 feet for braking and the total distance is 450 feet. It takes about 12 seconds to stop comfortably. Now factor in that most signals are across the intersection another 50 feet away. You need to be able to see the signal change from green to yellow while almost 500 feet away. Do you see why you should not follow that semi-trailer too closely and why state law says yellow means slow to a stop, not punch it?

            Many traffic jurisdictions have added a second or two to the red signals after the amber light to allow the intersections to clear out before cross-traffic starts moving. This will help drivers “too close when the yellow light comes on so they figure they must go through.” Problem solved, right?  No! What we find is that the wise guys/smart alecks become aware that they can get away with more.