So I got a ticket a few days ago for running a red light, the yellow light was very short, I'm trying to figure out if the city set the yellow light too short to be reasonable.(adsbygoogle = window.adsbygoogle || []).push({});

The speed limit at that location is 50 mph, the yellow light is 4 seconds.

Federal motor vehical safety standards specify that a vehical must be able to stop from 62 mph in 230 feet.

Stopping distance = Average speed during stop x time spent stopping

At constant deceleration average speed during stop = 1/2 initial speed

62 mph = 91 fps

so...

230=(1/2)*91*t

230=45.5*t

t=5 seconds

Stopping from 50 mph instead of 62 should take 50/62 of the time, or 4 seconds. This is exactly the duration of the yellow light so stopping in time would require instant reaction to the light turning yellow. Instant reaction is impossible for a human so the light is unreasonably short.

On the other hand...

50 mph = 73 1/3 fps

73 1/3 fps * 4 seconds = 293 1/3 feet so I should have been at least that far from the light when it turned yellow. Since my stopping distance from 50 mph is shorter then my stopping distance from 62 mph I should have had > 63 feet to react to the light.

I don't see a flaw in either line of reasoning but they obviously contradict each other. Where is my error?

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# Trying to find the error in my logic or math. Deceleration of a car.

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