All real estate taken or held under sections 40:37-96 to 40:37-174 of this title for the purpose of public parks shall be forever kept open and maintained as such, and no steam or other railroad shall be laid out on, or maintained or operated in or on any portion of the parks, open spaces, boulevards, parkways or roadways laid out and located under said sections 40:37-96 to 40:37-174, except at such places and in such manner as the commission shall in writing approve.