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Friday, December 4, 2009

Letter Writer Wants Longer Yellow Lights

Coeur d'Alene Press Letter To The Editor:

I write this letter to the editor hoping that it will reach the eyes of whichever authority has jurisdiction over the traffic signals at the 95-Prairie intersection. Surely I am not the only one who thinks this issue needs addressing. It has to do with the length of time the signals show yellow before they change to red.

Traveling south on US 95 at the Prairie Ave. intersection: The yellow signal lasts approximately four seconds. I timed it for five cycles. The times ranged between 3.46and 3.88 seconds.

In four seconds a car moving at the posted speed limit (45 MPH) travels 264 feet, 66 feet per second.

According to the Idaho Driver's Handbook: At 45 MPH it takes 101.5 feet to react to the light changing.

It takes an additional 114 feet to bring the car to a stop. A quote from the handbook: "Total minimum stopping distances with perfect 4-wheel brakes on the best type of road surface under favorable conditions."

I wish to point out that for all intents and purposes, the 215.5 feet allotted amounts to a panic stop, and not the type of stopping drivers should be faced with in normally reacting to traffic signals.

The 101.5 reaction distance does not factor in the judgment time necessary to calculate your distance from the limit line, weather factoring, whether the stop can be made safely or any other of the multitude of calculations necessary to safely stop the vehicle. The allotted 101.5 feet only provides for the reaction time for a panic stop. The 114 feet stopping distance applies only to a panic stop.

The foregoing indicates that four seconds is an insufficient amount of time to bring a car to a safe stop if the car is 264 feet or nearer to the intersection when the car is traveling at the posted speed limit of 45 MPH. Even one additional second or five seconds total would be a vast improvement.

Dalton Gardens

Um... I'm not really sure where to go with this. Do you agree/disagree? Are you surprised that Mr. Barbieri did this much research to write a letter to the editor?


Terry Harris said...

The math may very well be correct -- I didn't check, but he might have reached the wrong conclusion. Rather than increase the time for yellow -- which is typically 3-4 seconds -- the simplest solution might be to lower the speed limit.

KMPO Staff said...

You may be onto something there Terry. In my experience, a lot of people use the yellow light to bail through the intersection at the last possible moment, so giving them another second would just let another car through the intersection. Slow the speed limit though and it takes less time to stop and may improve the safety of the intersection. Thanks for pointing out that there could be another way to go about fixing an issue like this Terry.