§ 1645. Exempting fuel oil trucks from use of truck routes in cities having a population in excess of one million. No ordinance, order, rule or regulation made by the legislative body of any city having a population in excess of one million shall require any fuel oil truck to use a designated truck route while such fuel oil truck is being used to make deliveries to a heating oil customer or is returning to the place of business of the owner of such fuel oil truck immediately after having made a delivery to a heating oil customer.