Gear for going off motorway: heading to junction going around slow-moving traffic (3-4)
I believe the answer is:
'gear for going off' is the definition.
(pyjamas - clothes worn when going off to sleep)
'motorway heading to junction going around slow-moving traffic' is the wordplay.
I cannot quite understand how this works, but
'motorway' could be 'm' (as in motorway names - M1, M4 etc) and 'm' is found in the answer.
'traffic' could be 'jam' (I have seen 'awful traffic' mean 'jam' so perhaps 'traffic' could also mean 'jam') and 'jam' is present in the answer.
This may be the basis of the clue (or it may be nonsense).