Preserve a lot of traffic (3)
I believe the answer is:
jam
I believe this clue is a triple definition!
'preserve' is the first definition.
(jam is a kind of preserve)
'a lot' is the second definition.
(thesaurus)
'of' is a link.
'traffic' is the third definition.
(I have seen 'awful traffic' mean 'jam' so perhaps 'traffic' could also mean 'jam')
(Other definitions for jam that I've seen before include "Troublesome situation" , "Preserve; pack tightly" , "Preserve - predicament" , "awful traffic" , "Block signals" .)