They may permit, regulate or prohibit the locating, constructing or laying of the tracks of any railroad, or tramway in any street, alley or public place; and may by ordinance grant franchises to railroad and street railroad companies, and to union railroad depot companies, to lay, maintain and operate in any street or part or parts of streets or other public places tracks therefor, but such permission may not be exclusive or for a longer time than 100 years.