On motorway, coming into certain disaster (12)
I believe the answer is:
misadventure
'disaster' is the definition.
(I've seen this before)
'on motorway coming into certain' is the wordplay.
'on' is a charade indicator (letters next to each other).
'motorway' becomes 'mi' (resembles Ma, English motorway).
'coming' becomes 'advent' ('advent' can be a synonym of 'coming'**).
'into' means one lot of letters goes inside another.
'certain' becomes 'sure' ('sure' can be a synonym of 'certain').
'advent' inserted into 'sure' is 'sadventure'.
'mi' put next to 'sadventure' is 'MISADVENTURE'.
(Other definitions for misadventure that I've seen before include "Unfortunate incident" , "Accident" , "Mishap" , "disaster" , "Bad luck; accidental killing" .)