Vehicle fuel production is prudent (7)
I believe the answer is:
careful
'prudent' is the definition.
(associated in meaning)
'vehicle fuel production' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'production' is an anagram indicator.
'fuel' is an anagram of 'eful'.
'car'+'eful'='CAREFUL'
'is' is the link.
(Other definitions for careful that I've seen before include "Painstaking" , "Diligent" , "Attentive" , "Watch it!" , "'Prudent, cautious (7)'" .)