The city council, by resolution, shall designate truck routes for movement in the city of commercial vehicles exceeding a maximum gross weight limit of five tons, and when so designated by an appropriate sign, the operator of each such vehicle shall drive on such route or routes and none other except when necessary to go by direct route on restricted streets to make pickups or deliveries of goods, wares and merchandise or to deliver materials for the repair, alteration, remodeling or construction of any building or structure for which a building permit has previously been obtained. This section shall not apply to passenger buses under the jurisdiction of the Public Utilities Commission, or to any vehicle owned by a public utility that is currently being used in the construction, installation or repair of any public utility, or to any on-call tow vehicle designated pursuant to Section 14-1-18 of this code. (Ord. No. 938, § 1; Ord. No. 1457, § 3 (part).)