You got a ticket for running a red. Here's why that yellow light might have seemed short | CBC Radio

Traffic lights require split-second decisions based on distance, time, velocity, and driver behavior. Yellow (amber) timing and the all-red period are programmed using accepted guidance that accounts for approaching vehicle speed, deceleration rates, and road slope. Driver reaction time is also included in the calculations. Each intersection is treated as a unique case, with traffic engineers examining topography and the speed limit on the road segment before setting how long drivers see yellow. If stopping safely is possible when the light turns yellow, drivers should stop. If stopping in time is not possible and entry is required, drivers would still enter only when it is necessary and safe to do so.

"The traffic light turns from green to yellow, and you're called upon to perform calculus involving distance, time, velocity and the presence of tailgaters. It's a lot of variables. Get it wrong and you could wind up with a red-light camera ticket get it catastrophically wrong and you could wind up in an accident."

"Jodie Marcyniuk, acting senior leader for traffic management at the city of Calgary, says her department follows accepted guidance for calculating the timing of amber lights, as well as the period of all red. That's the short time when cars in all four directions face red and no vehicles can go."

"These recommendations rely on basic high school physics, she says. It's looking at speed of approaching vehicles. It's looking at deceleration rates. And it's looking at slope of the road, she says. And then it also considers driver reaction time. That means that every intersection is treated as a unique case, Marcyniuk says, with traffic engineers examining things like the topography and the speed limit on that stretch of road before deciding how long drivers will see that yellow light."

"Marcyniuk says if you can stop safely when the light turns yellow, you should. But if you're running late for work, the family potluck or your kid's gymnastics class, it's easy to forget the general principle behind yellow lights. If you can't stop in time, if you do need to enter the intersection, you would still be entering on ye"

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