Why should the trailer hand valve not be used to straighten a trailer jackknife caused by braking?
Correct answer: B – The trailer wheels are already skidding, and additional trailer braking will not restore traction
When trailer wheels lock during braking, the trailer can swing outward into a jackknife. The trailer hand valve applies only the trailer brakes, adding braking force to wheels that are already skidding. Release the brakes to regain traction; once the trailer wheels grip the road again, the trailer should begin following the tractor.
Source: Arkansas Commercial Driver’s License Manual — § 6.1.5, “Prevent Trailer Skids”

