Propagation rate through the brake pipe during an emergency reduction is:

Propagation rate through the brake pipe during an emergency reduction is:

• A. 540 ft/sec
• B. 930 ft/sec
• C. 600 ft/sec
• D. 1200 ft/sec

Answer: (B)

When an emergency reduction happens, the change in brake pipe pressure moves as a pressure wave along the train. This signal travels through compressed air in the pipe at a speed close to the speed of sound in air, so the announcement reaches the entire train very quickly. In practice, the propagation rate is about 900–1000 ft per second, with 930 ft/sec being a commonly cited value. That rapid spread is what makes the brake response appear nearly instantaneous from car to car. The other speeds are outside these typical propagation ranges, so 930 ft/sec best matches how fast the emergency signal actually travels.

When an emergency reduction happens, the change in brake pipe pressure moves as a pressure wave along the train. This signal travels through compressed air in the pipe at a speed close to the speed of sound in air, so the announcement reaches the entire train very quickly. In practice, the propagation rate is about 900–1000 ft per second, with 930 ft/sec being a commonly cited value. That rapid spread is what makes the brake response appear nearly instantaneous from car to car. The other speeds are outside these typical propagation ranges, so 930 ft/sec best matches how fast the emergency signal actually travels.