Decision put off people crossing major route (13)
I believe the answer is:
determination
'decision' is the definition.
(I know that decision can be written as determination)
'put off people crossing major route' is the wordplay.
'put off' becomes 'deter' (both can mean to discourage).
'people' becomes 'nation' ().
'crossing' is an insertion indicator (to cross can mean to go over or around).
'major route' becomes 'mi' (resembles Mn, English motorway).
'deter'+'nation'='deternation'
'deternation' placed around 'mi' is 'DETERMINATION'.
(Other definitions for determination that I've seen before include "Resolution" , "Decision process" , "24 [DRIVE]" , "Willpower" , "Firmness of purpose" .)