Simple crash involving vehicles blocking bridge (7)
I believe the answer is:
spartan
'simple' is the definition.
(I've seen this before)
'crash involving vehicles blocking bridge' is the wordplay.
'crash involving vehicles' becomes 'RTA' (abbreviation for road traffic accident).
'blocking' indicates putting letters inside (block can mean to plug a gap in something).
'bridge' becomes 'span' (synonyms).
'rta' going within 'span' is 'SPARTAN'.
(Other definitions for spartan that I've seen before include "Lacking comfort or luxury" , "Old citizen" , "austere old Greek" , "Simple and harsh, without luxuries" , "Plain" .)