stale green
n. A traffic light that has been green for a long time and so is likely to turn orange at any moment.

Example Citation:
"Saunders said a leading exit ramp danger is what he calls the 'stale green' on the traffic signal at the end of the ramp.

'Drivers are tooling down the ramp and see a green light. So instead of backing off, they hold their interstate speed. The light changes and the car in front of them stops, and you have a crash. We see several fresh sets of skid marks on those ramps every day,' Saunders said."
—Tom Brennan, "Caution: Exit ahead," The Tampa Tribune