Practice question

Why should you never use the trailer hand valve (trolley brake handle) to park a tractor-trailer combination?

  1. It causes the trailer refrigeration unit to stall
  2. Air can leak down over time, causing trailer service brakes to release and allowing the unattended vehicle to roll away
  3. It discharges the tractor starter battery
  4. The hand valve can only be used when moving at speeds over 100 km/h

Answer: B — Air can leak down over time, causing trailer service brakes to release and allowing the unattended vehicle to roll away

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