Notwithstanding the provisions of section 14-267a, a motor vehicle which is owned or operated by any person, firm or corporation engaged in the business of collecting refuse and which is operated for the purpose of collecting such refuse or which is owned and operated by any town or municipality for such purpose, may be operated on any road or highway, if the axle weight on the rear axle or axles of such vehicle does not exceed the weight limits established pursuant to section 14-267a by more than seven thousand pounds and if the combined weight on the rear axles does not exceed forty-four thousand five hundred pounds. This exemption shall not apply to any such motor vehicle operated on any road or highway which is a part of the interstate highway system.