Casual walker taking left gets to a traffic light (5)
I believe the answer is:
amber
'to a traffic light' is the definition.
(I've seen this before)
'casual walker taking left' is the wordplay.
'casual walker' becomes 'ambler' (to amble is to walk casually).
'taking' suggests deleting specific letters.
'left' becomes 'l' (common abbreviation).
'ambler' with 'l' taken away is 'AMBER'.
'gets' is the link.
(Other definitions for amber that I've seen before include "Girl" , "A yellowy resin" , "Prepare-to-stop signal" , "Name of female" , "warning signal" .)