[supercat]

I think everyone does the "timing" thing to some extent, and it's actually prtty smart if done conservatively as a means to avoid excess braking and accelerating, so we agree there. If there's any aspect of the practice that might be illegal, it would be the case where someone's crossing the limit line at or above the posted limit just as the light goes green, and it would only be illegal owing to the elevated risk that such a vehicle would be exposed to a substantively elevated risk of getting t-boned by inattentive cross trafffic blowing their red light.

If I were a cop with a radar and video camera, and were interested in ticketing dangerous motorists, I would issue tickets to motorists who, at any time while the light was red or there was traffic in the intersection that did not have enough momentum to clear it, would not have been able to stop safely before the intersection had the light remained red or the motorists therein not gotten clear. I'd be fairly nice and assume motorists were capable of 1.5g braking (which is pretty hard).

The safe way to time a light is to slow down enough that when the light is expected to turn green you'll still be far enough away from the intersection when the light is expected to turn green that you'll still be able to stop if for whatever reason it does not.

[HKMk23]

...you'll still be far enough away from the intersection when the light is expected to turn green that you'll still be able to stop if for whatever reason it does not.

The one unresolved question is: "Is it illegal to time triffic lights in a manner that is out of line with the criteria you set forth?"