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