It was easier in Brampton to call it Highway 10, as it has two names - Main Street in the old Town of Brampton boundaries, and Hurontario outside of them (just like it's Queen Street rather than Mississauga Road in the old Streetsville boundaries). Hurontario Street came before Highway 10, and was part of that early road system that pre-dates the concession plan. Now that most references to Highway 10 are gone (thank you, Harris and Palladini!), these directions don't work so well.
Queen Street East of 410 is still well-known as Highway 7, oldtimers call Bovaird west of 410 Highway 7 Bypass. I still like to call "Heritage Road" 5th Line West (legally, it is 5th Line W.H.S. - a legacy of imposing the concession system on the original road network).
In Toronto, these pre-concession roads include Danforth Road, Kingston Road, Yonge Street, Albion Road, Davenport Road, Dundas Street; Other fairly well-known ones include Elora Road, old Highway 8 in Niagara, Garafraxa Road (Highway 6 north of Guelph), Huron Road (Highway 8 between Stratford and Goderich), and so on.