The air brakes used on heavy vehicles (semi trucks, etc) have a very simple fail-safe. You need power to not brake. I.E. Air pressure is used to disengage th

The air brakes used on heavy vehicles (semi trucks, etc) have a very simple fail-safe. You need power to not brake. I.E. Air pressure is used to disengage the brakes. If you lose power/air pressure, the brakes engage and are stuck engaged.