It varies by state. In oregon, you must technically stop at the yellow and then may proceed if it is safe. In texas, you may proceed thru the yellow but have been warned that a red is coming.
If your rear wheels cross the line before the light turns red, then you did not run the light. If your rear or front wheels cross the line after the light turns red, you ran it. My experience as a juror in a red light case also backs this up.
If you have a trailer, it's wheels also count.
Here is a big one that I wish more people knew...
In most states, when desiring to turn and facing a green light, the first car should proceed into the intersection. Then it may turn when safe or the light turns red.
Note-- this guarantees at least one car gets to turn per signal change!
---
Interesting bits here:
http://www.popularmechanics.co...
Red light camera contracts are very expensive to exit early.
Red light cameras are inaccurate even when the city's not cheating (ticketing a parked car shown to be parked).
Red light cameras trade T-Bone collisions for increased rear end collisions.
Red light cameras generate a lot of false positives from legal right turns on red. This overloads the court system or creates the need for employees to pre-check each ticket before it is sent out. Which wipes out the income or creates losses.
Finally, if you google "red light camera fast yellow", you'll find numerous examples of cities that cheated by making yellow lights shorter (in some cases too short to humanly react before it turned red). Apparently florida has had a lot of problems lately.
