Section 6. Every corporation undertaking to perform in public ways the kind of public service authorized by this chapter shall first procure a permit from the authorities having jurisdiction over such public ways in the manner prescribed in and in accordance with section seven of chapter one hundred and sixty-one, and the granting of such permit shall be subject to the approval of the department as provided in said section for the location of street railways. The fee for such a permit shall be set by the authorities having jurisdiction over such public ways. No such approval shall be given for any line any part of which, in the opinion of the department, is so nearly contiguous or adjacent to the line of a street railway company that its construction would result in a competitive service injurious to the public and to such street railway company: provided, that the latter is ready and willing and offers to construct and does construct, within such reasonable time as the department may fix, a line of street railway or a line of trolleymotor or trackless trolley in the public way described in the petition, which the department deems will serve the public as well as would the proposed line described in the petition; and no such approval shall be granted in any event if the department deems that the granting of the same would be unduly injurious to any street railway or trackless trolley line covering the same or substantially the same territory.