Vehicle requiring endless caution (3)
I believe the answer is:
car
'vehicle' is the definition.
(I know that car is a type of multi-track vehicle)
'endless caution' is the wordplay.
'endless' means to remove the last letter.
'caution' becomes 'card' (I've seen this before).
'card' with its final letter taken off is 'CAR'.
'requiring' acts as a link.
(Other definitions for car that I've seen before include "Auto" , "Private vehicle" , "Wheels" , "Four-wheeled vehicle" , "Railway carriage; vehicle" .)