§ 209. Change of motive power authorized. Any railroad company having the right to use any railroad now constructed in any public tunnel, road or way depressed below the surface of and wholly within any public park in any city within the state of New York having a population of one million five hundred thousand or upwards, may change the motive power and operate any such railroad by cable power, underground current of electricity, compressed air, or any other motive power other than locomotive steam power that may be consented to by the authorities having control of such park or parks, and by the commissioner of transportation, and may make changes in the construction of the road or roadbed or other property made necessary by the change of motive power. Such reconstruction shall be at the sole cost and expense of the railroad company making such change, and when completed such improved railroad shall be the property of the municipal corporation having control of such public tunnel, road or depressed way.