N.Y. Railroad Law § 240

§ 240. Gates or vestibule doors. Every car used for passengers upon\nelevated railroads shall have gates at the outer edge of its platforms\nso constructed that they shall, when opened, be caught and held open by\nsuch catch or spring as will prevent their swinging and obstructing\npassengers in their egress from or ingress to such cars, or vestibule\ndoors so constructed as to slide into the body of the car; and every\nsuch gate or door shall be kept closed while the car is in motion; and\nwhen the car has stopped and a gate or door has been opened, the car\nshall not start until such gate or door is again firmly closed.\n