The emergency portion of each triple valve is activated by the higher rate of reduction of brake pipe pressure. Due to the length of trains and the small diameter of the brake pipe, the rate of reduction is highest near the front of the train (in the case of an engine operator-initiated emergency application) or near the break in the brake pipe (in the case of loss of brake pipe integrity). Farther away from the source of the emergency application, the rate of reduction can be reduced to the point where triple valves will not detect the application as an emergency reduction. To prevent this, each triple valve's emergency portion contains an auxiliary vent port, which, when activated by an emergency application, also locally vents the brake pipe's pressure directly to atmosphere. This serves to more rapidly vent the brake pipe and hasten the propagation of the emergency reduction rate along the entire length of the train.