Truck Crash Reference

Jackknife crashes

Last updated . Sources checked

Contents
  1. How alignment is lost
  2. What anti-lock brakes do
  3. Questions for reconstruction
  4. Related entries
  5. References
Jackknife crashes
Vehicle configurationTractor and trailer combination[1]
Safety systemABS reduces wheel lockup; it does not eliminate skid risk[1]

A jackknife is a loss-of-control configuration in which a tractor and trailer move out of alignment and fold toward one another. The Oregon commercial driver manual distinguishes tractor skids from trailer skids. That distinction matters because the vehicle that first loses traction can require a different explanation from the final position of the combination.[1]

See: FMCSA and federal trucking rules

How alignment is lost

The combination-vehicle manual explains that when trailer wheels lock, the trailer tends to swing around. It notes that this is more likely with an empty or lightly loaded trailer. Its ABS guidance separately discusses loss of steering control and a tractor jackknife. A photograph of a folded rig shows the resulting configuration, but it does not establish which unit first lost control.[1]

What anti-lock brakes do

Anti-lock braking systems are intended to prevent wheel lockup during hard braking. The driver manual cautions that ABS does not necessarily shorten stopping distance and does not make a vehicle immune to skids. It describes different braking guidance for a combination depending on which units have ABS. Equipment configuration must therefore be established rather than inferred from the tractor alone.[1]

Questions for reconstruction

The manual links trailer wheel lockup to a swinging trailer and describes maintaining control during braking. A reconstruction can use those mechanisms as questions to test against the physical record: where the combination began rotating, which unit moved sideways and what steering or braking preceded it. The term jackknife describes the movement; it should not substitute for evidence about the driver action or mechanical condition that initiated the event.[1]

References

  1. abcdef Oregon Commercial Driver Manual: Combination Vehicles. Oregon Department of Transportation. https://www.oregon.gov/odot/DMV/Pages/Online_CDL_Manual_2/Section_6.aspx. official. Checked . Source record