Mo. Rev. Stat. § 82.250: Certain cities may acquire subways.

All cities in this state having one hundred thousand inhabitants or over are hereby authorized and empowered to build or to acquire, by purchase or otherwise, within their respective corporate limits, a subway or subways, to be exclusively owned by such cities, with such suitable approaches, connections, loops, turnouts, sidings, stations, exits, entrances and other appurtenances, and land, rights-of-way and easements and estates and rights in land, including the right to go on, under or above the surface, as may be necessary or expedient for the construction and efficient use of such subway or subways for the transportation of persons, baggage, express and freight, and for cars, other means of transportation, pipes, wires and cables used for public service purposes.