Tire and tell the driver to stop (4)
I believe the answer is:
flag
'tire' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for flag that I've seen before include "slow down" , "National emblem; tire" , "Droop; iris" , "Iris; ensign" , "variety of plant" .)