The limitations as to the length of vehicles and loads stated in § 31-25-5 and § 31-25-6 shall not apply to any load upon a pole trailer as defined in § 31-1-5 when transporting poles or pipes or structural material which cannot be dismembered, provided that no pole or pipe or other material exceeding eighty feet (80?) in length shall be so transported unless a permit has first been obtained as authorized in § 31-25-21.