No right shall be given by municipal or county authorities to occupy the track, single or double, or other structure, of existing street railways for more than one eighth of the distance between the termini of the route, as actually constructed, operated, and run over, of the company or person to whom such grant is made. In granting permission to extend existing routes in cities, the cities and companies owning such route shall have all the rights and powers which they possess under existing laws and contracts.