Restrictive fifty on current motorway can start to gall (8)
I believe the answer is:
limiting
'restrictive' is the definition.
(similar in meaning)
'fifty on current motorway can start to gall' is the wordplay.
'fifty' becomes 'li' (I've seen this in other clues).
'on current motorway' becomes 'mi' (I can't explain this - if you can you should believe this answer much more).
'can' becomes 'tin' (synonyms).
'start to' says to take the initial letters.
The first letter of 'gall' is 'g'.
'li'+'mi'+'tin'+'g'='LIMITING'
Can you help me to learn more?
(Other definitions for limiting that I've seen before include "Checking" , "Bounding" , "Restricting scope or freedom" , "cutting back" .)