This week’s ‘Ask Evan’ question deals with traffic lights. Drew A asks, “Is the length of a yellow light regulated? Some traffic signals stay yellow for quite some time while others seem to be very short?"
I reached out to PennDOT for details and here’s what I’ve been told. The duration of yellow lights includes algebraic formulas and other deep details. Way too much to get into here, and frankly really understand! So, here’s the boiled down version from PennDOT.
Basically, timing on all traffic signals falls under the manual on uniform traffic control devices. They are all federally regulated, so every signal in the state is owned, operated and maintained by the municipality– but PennDOT sets all the timing. The yellow light is based on a variety of factors, including the incoming speeds to the intersection and the grade of the road — whether it is uphill or downhill. Typically a yellow light can be between 3 and 6 seconds based on those factors. Shorter being a slower speed like 25 mph, or on an uphill climb.
In fact, there is a move to make yellow lights even a bit longer, based on the ‘dilemma zone,’ which means the area where you make the decision between slamming on your brakes or speeding up to make it through the light, especially when the speeds are higher.
Some have long questioned the length and fairness of yellow lights.. Especially when it comes to being cited for running a red light– because the yellow light seemed short.