For the purpose of constructing and maintaining such lines of telegraph or telephone, the parties in interest may set the necessary poles or posts on which to place the wires and insulators of such lines, in any of the public streets, highways or alleys, or in any private road leading to such highways, streets or alleys outside of the incorporated cities, villages or towns in this state along which such lines may pass: Provided, such poles or posts shall be placed along the boundaries of such highways, streets, or alleys, at such distances therefrom as the authorities having control thereof may direct. And provided further, that the wires necessary for such lines shall not be less than fifteen feet above the ground along such boundaries, and not less than twenty feet at any public or private crossing, and shall be so placed as not in any manner to interfere with such crossing.