Stop working on highway (4)
I believe the answer is:
rest
'stop working' is the definition.
'rest' can be an answer for 'stop' (thesaurus). I am unsure of the 'working' bit.
'on highway' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'highway' becomes 'st' (I am not sure about this - if you are sure you should believe this answer much more).
're'+'st'='REST'
Can you help me to learn more?
(Other definitions for rest that I've seen before include "'Relax, pause from work (4)'" , "Leisure" , "Relax, take a break" , "Repose - remainder" , "Change is as good as this, they say" .)