Planning Act vs Highways Act - Public forum - Planning Advisory Service (PAS)

Is it possible to do a legal agreement under the planning act which would take away powers under S37 of the Highways Act for residents to petition the Highway Authority to adopt a road? I am unsure if a legal agreement under one piece of legislation can override that of another piece of legislation... We are trying to do a private roads agreement, which would prevent residents making us adopt the road in the future. Thanks