Section 2. Every such license shall specify the route or routes over which the motor vehicles used thereunder may be operated, and shall be on a form approved by the department of telecommunications and energy; provided, that a variance from a form so approved shall not affect the validity of the license if the form used is in substantial conformity with the approved form. A licensee shall not operate motor vehicles for the purposes specified in section one otherwise than upon routes specified in the license or licenses issued to him; provided, that in the event of the closing of the whole or a portion of such a route by public authority or of interference with operation thereon by street repairs, fire, accident, unusual and severe traffic congestion or other emergency, a licensee may temporarily operate such vehicles by a reasonably direct and convenient detour.