[Renfield]

Air brakes are “negative”, which means that air pressure keeps the brakes off, not on. Loss of air pressure locks up the brakes.

[The Cajun]

Air brakes are “negative”, which means that air pressure keeps the brakes off, not on.

Was wondering if trains were like 18 wheelers.
On our big rigs we had *Maxi brakes*, when you would set them, you pulled a knob which would bleed off air pressure with a pretty loud sound to it.

[Balding_Eagle]

Not so. Air pressure is required to keep the brakes on.

http://www.freerepublic.com/focus/f-news/3041105/posts?page=12#12