County commissions in counties of this state which now have, or may hereafter have, over fifty thousand inhabitants according to the last preceding census, where any such county is adjacent to a city of over six hundred thousand inhabitants, are hereby authorized to establish public roads less than thirty feet in width or accept, in whole or in part, as public highways, roads already established where the same parallel and abut upon either side of the rights-of-way of steam railroads, electric or interurban railroads and the two roads aggregate not less than fifty feet in width.