Come across motorway, with help for driving northwards (4)
I believe the answer is:
meet
'come across' is the definition.
(synonyms)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for meet that I've seen before include "Join" , "Confront" , "Encounter - suitable - pay" , "Come across" , "Sporting encounter" .)