HOW IT ALL WORKS - All Aboard: The Complete North American Train Travel Guide - page 170

Stopping a Train
Being able to stop a train is critically important and can be a
tricky thing to do. It is, after all, a massive amount of moving
weight and sometimes moving at high speed. For example, an
eight-car passenger train traveling at 80 miles per hour requires
a minimum of three-fourths of a mile to stop, even under emer-
gency braking conditions. Much greater weights are involved
with freights; as would be expected, they are that much more
difficult to stop. A 100-car freight train can weigh more than
10,000 tons and, even traveling at just 30 mph, will simply not
be able to stop in less than one mile.
There's really only one way to stop any rolling vehicle—by
applying pressure against the wheels. That's the way we stop
cars, and it's the way trains are stopped too. There is a brake on
every wheel of every car of every train.
Braking was done manually on the earliest trains, but it
wasn't until about 1900 that air brakes became standard equip-
ment on all railroad cars, whether freight or passenger. The air
brakes on every car in the train are controlled by the engineer
from the locomotive cab, although, in an emergency, the conduc-
tor can activate the brakes from anywhere on the train.
The brakes are operated by using compressed air carried
throughout the train by hoses that are connected when any two
cars are coupled together. The first air brakes used the com-
pressed air to force the brake shoes against the wheels. That
method worked well as long as nothing went wrong. But if the
air compressor failed or if a hose broke anywhere along the
train, the resulting loss of air pressure meant the entire brak-
ing system failed, which lead rather quickly to spectacularly
unpleasant consequences. Then in 1887 in Burlington, Iowa,
George Westinghouse had a very simple but very bright idea:
instead of using the air pressure to force the brake shoes against