False report prison to be located over a road (6)
I believe the answer is:
canard
'false report' is the definition.
(a canard is a false rumour or story)
'prison to be located over a road' is the wordplay.
'prison' becomes 'can' (the can is American slang for prison).
'to be located over' means one lot of letters go next to another (in a down clue, some letters go on top of others).
'road' becomes 'rd' (abbreviation).
'can'+'a'+'rd'='CANARD'
(Other definitions for canard that I've seen before include "Ugly rumour" , "Unfounded rumour or story" , "False rumour, originally from France" , "rumour that's false" , "A false rumour from France? (6)" .)