International trains crashing en route (2,7)
I believe the answer is:
in transit
'en route' is the definition.
(I've seen this before)
'international trains crashing' is the wordplay.
'international' becomes 'int' (abbreviation for international).
'crashing' indicates an anagram.
'trains' anagrammed gives 'ransit'.
'int'+'ransit'='IN TRANSIT'
(Other definitions for in transit that I've seen before include "On its way" , "While being conveyed" , "on the move?" , "En route" , "during journey" .)