An article on The Drive started me down the rabbit hole. Interesting how important yellow light length is to preventing accidents at intersections. I wonder if most yellows are timed to go with the speed limit, or the actual speed that the majority of drivers go through intersections (varies greatly, I’m sure). Clearly, it should be the latter. 

Found this:

Minimum Yellow Light Times

The following table of actual vehicle approach speed vs. minimum yellow light times is a result of calculating the yellow interval duration per the ITE-proposed formula (shown in the next section of this page) and rounding up the result to the nearest half second. These yellow light times are not statutory requirements that can be used as a defense in a court of law. But they do provide a rule-of-thumb when initially evaluating whether a traffic signal’s yellow light timing is possibly deficient. Note that these intervals are for normal passenger cars traveling in through, i.e., non-turning, lanes. They are not adequate for turn lanes or special cases such as heavy trucks or buses.

The Federal Highway Administration’s Manual on Uniform Traffic Control Devices provides guidance that the yellow interval be between three and six seconds without tying the requirement to specific approach velocities. That said, anything falling below the yellow times shown here should be considered as a potential short yellow light.

25 MPH — 3.0 Seconds
30 MPH — 3.5 Seconds
35 MPH — 4.0 Seconds
40 MPH — 4.5 Seconds
45 MPH — 5.0 Seconds
50 MPH — 5.5 Seconds
55 MPH — 6.0 Seconds