Traffic needs to speed up heading for Edinburgh (5)
I believe the answer is:
trade
'traffic' is the definition.
(thesaurus)
'to speed up heading for edinburgh' is the wordplay.
'to speed' becomes 'dart' (darting is a kind of speeding).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'heading for' indicates taking the first letters.
The initial letter of 'edinburgh' is 'e'.
'dart' back-to-front is 'trad'.
'trad'+'e'='TRADE'
'needs' is the link.
(Other definitions for trade that I've seen before include "Customers" , "Commercial dealings" , "Barter, do business" , "job" , "groundsman?" .)