prevented tampering or error. The button boards were equipped with an indication flag which told the conductor when all doors were finally closed. As mentioned above, each car as delivered required its own conductor to operate doors. During the 1919–20 modifications, the cars were unitized into new arrangements (see letter designations below) and converted to allow one conductor to control an entire train's doors. This made operation of the cars more efficient, and reduced labor costs. Like all previously designed subway cars, A/B Standards featured end storm doors for riders to pass between cars. However, due to the car's longer 67-foot length and resultant overhang, crossing between cars was dangerous, particularly on curves. Therefore, storm doors were kept locked on these cars, although in emergencies, they could be opened pneumatically by the conductor from the button board. For emergencies, the cars also featured emergency brake cords like other subway cars, but added an emergency alarm which could be activated to notify the train crew in case of emergency. Electric tail lights and running lights were introduced to the subway with the A/B Standards. Low running lights would display white at the front of the train, while tail lights displayed red in the rear. This feature was directly connected to the motorman's reverser control. This was in contrast to the IRT practice of using kerosene lamps at the ends of trains, which had to be physically changed over when the train reversed direction at a terminal. At the time the A/B Standards were delivered, the white running lights were deemed sufficient for lighting tunnels. However, during the 1950s, the New York City Subway made a system wide shift to sealed beam headlights to improve safety. Therefore, those that received overhaul from 1959 to 1962 (cars 2400–2799 and 2899) received sealed beams. Coupling and uncoupling of trains were simplified by new automatic couplers. The new WABCO couplers automatically made and broke electric and air connections as trains were coupled or uncoupled. This reduced the amount of work for train crews during the process. For example, IRT crews had to physically connect or disconnect high voltage jumper cables when coupling or uncoupling their trains. BRT/BMT crews on A/B Standards did not. The only jumper such a crew would ever have to connect or disconnect was the 9 point low voltage jumper introduced with the 1919–1920 modifications. Coupling and uncoupling, therefore, were much simpler