Split when the vehicle overturns (4)
I believe the answer is:
part
'split when' is the definition.
'part' can be an answer for 'split' (synonyms). I am unsure of the 'when' bit.
'vehicle overturns' is the wordplay.
'vehicle' becomes 'trap' (trap is a kind of vehicle).
'overturns' says the letters should be written in reverse.
'trap' back-to-front is 'PART'.
'the' is the link.
Can you help me to learn more?
(Other definitions for part that I've seen before include "unemployed actor hopes for" , "Portion of a whole" , "Constituent - something to play?" , "Sever; portion" , "Fraction of the whole - separate" .)