They reflect action sure to curb traffic primarily (4-4)
I believe the answer is:
cats-eyes
'they reflect' is the definition.
(cat's-eyes are reflective road features)
'action sure to curb traffic primarily' is the wordplay.
'action' becomes 'case' (synonyms).
'sure' becomes 'yes' (both are affirmative answers).
'to curb' indicates putting letters inside (curb can mean to restrain or contain).
'primarily' suggests taking the first letters.
The first letter of 'traffic' is 't'.
'case'+'yes'='caseyes'
'caseyes' enclosing 't' is 'CATS-EYES'.
(Other definitions for cats-eyes that I've seen before include "Road safety devices" , "Middle-of-the-road reflectors" , "Light-reflecting studs set into road" , "On the road, they reflect light" , "Line of reflective studs as road markings- very feline" .)