When any truck route is established and designated by appropriate signs, the operator of any vehicle exceeding a maximum gross weight limit of three tons shall drive on such route and none other; except, that nothing in this Section shall prohibit the operator of any vehicle exceeding a maximum gross weight of three tons coming from a truck route having ingress and egress by direct route to and from restricted streets when necessary for the purpose of making pickups or deliveries of goods, wares and merchandise from or to any building or structure located on such restricted streets, or for the purpose of delivering materials to be used in the actual and bona fide repair, alteration, remodeling or construction of any building or structure upon such restricted streets for which a building permit has previously been obtained therefor.