Drivers, one prevaricating about vehicle on track (7)
I believe the answer is:
railcar
'vehicle on track' is the definition.
'drivers one prevaricating about' is the wordplay.
'drivers' becomes 'rac' (I've seen this in other clues).
'one prevaricating' becomes 'liar' (to prevaricate is to speak dishonestly).
'about' says the letters should be written in reverse.
'rac'+'liar'='racliar'
'racliar' back-to-front is 'RAILCAR'.
(Other definitions for railcar that I've seen before include "form of transport" , "vehicle on the line?" , "Passenger vehicle" , "Powered train unit" , "It's found on tracks" .)