” The train’s pneumatic brakes, which run on compressed air and are the first line of defense, had been shut down by firefighters when they switched off an engine that had caught fire after the engineer left.
It is not yet clear what caused the fire, but the shutting down of the engine prompted the pneumatic braking system to gradually leak air and lose its track-gripping power.”
On a truck you set the brakes and the spring brakes apply the pressure. You can bleed off all the air and the brakes stay on. All of ours had spring brakes on all four drivers. The trailers didn’t have them.