Maximum term of public utility franchises in cities and towns having population of six thousand or more.

No city or town having a population of more than six thousand shall have authority to grant to any person, firm, corporation, or association the right to use its streets, avenues, alleys, or public places for the construction or operation of water works, gas works, telephone or telegraph line, electric light or power plants, steam or other heating plants, street railroads, or any other public utility, except railroads other than street railroads, for a longer period than thirty years.