Vehicle holds back progress? Not true (5)
I believe the answer is:
bogus
'not true' is the definition.
(I've seen this before)
'vehicle holds back progress?' is the wordplay.
'vehicle' becomes 'bus' (public transport vehicle).
'holds' is an insertion indicator.
'back' says the letters should be written in reverse.
'progress?' becomes 'go' (progressing is a kind of going).
'go' backwards is 'og'.
'bus' going around 'og' is 'BOGUS'.
(Other definitions for bogus that I've seen before include "Dummy" , "that's not real" , "Mock" , "Sham, counterfeit" , "Fake, sham" .)