Finishes off the main road bypass (4)
I believe the answer is:
ends
'finishes off' is the definition.
(to end something is to finish it)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for ends that I've seen before include "Extremities" , "They may justify the means" , "They may be made to meet!" , "'Goals, objectives (4)'" , "Wanting goals" .)