Air brakes use compressed air to allow trains to run much faster, reducing the cost of train rides. Before air brakes, train speeds were limited due to an inability to reliably slow them. Runaway trains were a real problem before air brakes limiting the speed and utility of trains.
Westinghouse innovated an airbrake for trains that functioned vastly better than prior braking methods, which were sometimes ineffective and could cause trains to derail. His air brakes allowed trains to travel faster and more safely. They quickly became an industry standard.
The Westinghouse air brake used an air reservoir connected to brakes on each car. The momentum of the cars filled or removed air from the reservoir, slowing the train or allowing it to move faster. Unlike prior systems, the air brake was far more reliable and far less prone to break.
Air brakes clamp down when they are unengaged; the air pulls them away from the wheel rather than forcing them to slow wheels down. Because of this, in the event of a failure the brakes would clamp down slowing a train, rendering them failsafe. In the event of a catastrophic failure, the worse that would happen is a train wouldn’t move.
Earlier brakes were pneumatic but the systems leaked and were prone to failure. Whereas pneumatic fluid once leaked must be manually refilled, a challenge on countless rail cars, air is infinite.
Air brakes remain in use today for heavy equipment, especially equipment that is coupled. Some trains continue using air brakes though many have transitioned to electrical brakes that can apply more measured force. Air brakes are also used on semi-trailer trucks.
While the brakes are mechanically failsafe, human error can defeat them. If an engineer purposefully changes air pressure in the valves, the brakes can release when they should clamp. This happened in a 1988 Paris train accident which killed 56 and injured 60 people.
Later in life, Westinghouse decided to diversify and partnered with Tesla to build AC electricity.