Red Light Vs. Yellow Light
You know you're thinking about it *way* too hard when you start contemplating the many possibilities of whether or not Elwood really ran a red light.
The State Troopers pull him over & accuse him of running a red light; Elwood protests that the light was yellow. Possibly...
1) He really did run the red light.
2) The light may not have changed from yellow to red until Elwood was already out in the intersection, by which point he couldn't have stopped anyway.
3) The light did not change from yellow to red until Elwood was already passing under it, causing it to appear as though he had run the red light.
4) The real reason the State Troopers pulled Elwood over was because they saw that he was driving a decommissioned police vehicle and thought something was wrong & just used the light issue as an excuse to pull him over.
Did I miss any? ;)