Section 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.