Sat at a red light (5)
I believe the answer is:
idled
'sat at a red light' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for idled that I've seen before include "(Of an engine) ran slowly out of gear" , "Wasted time" , "not worked" , "Lazed around" , "Turned over" .)