Makes slow progress on a street car (7)
I believe the answer is:
strolls
'makes slow progress' is the definition.
The definition and answer can be both to do with motion as well as being verbs in their -s form.
Perhaps you can see an association between them that I don't see?
'on a street car' is the wordplay.
'on' is a charade indicator (letters next to each other).
'a street' becomes 'st' (abbreviation).
'car' becomes 'rolls' (short for Rolls Royce).
'st' put next to 'rolls' is 'STROLLS'.
Can you help me to learn more?
(Other definitions for strolls that I've seen before include "Saunters" , "Walks" , "Takes a turn" , "Ambles" .)