Which emergency shutoff styles are used on DOT trailers?

• A. Pneumatic
• B. Hydraulic
• C. Cable
• D. Pneumatic, hydraulic, and cable

Answer: (D)

Emergency shutoff on DOT trailers can be implemented in a few different ways, depending on the braking system design. Pneumatic shutoffs use the air brake lines to rapidly vent or cut off pressure, causing the trailer brakes to engage or the system to isolate in an emergency. Hydraulic shutoffs operate the same idea for trailers that use hydraulic braking by stopping the hydraulic supply. Cable shutoffs are mechanical; a pull cable manually actuates a valve or lever to shut off the system. Because trailer designs vary, all three styles—pneumatic, hydraulic, and cable—are used, so the comprehensive option reflects the range of possible shutoff styles you might encounter.