SAE J1739
Definition
Society of Automotive Engineers standard for traffic-accident reconstruction covering momentum, skid, and crush-energy methods; the primary scientific-community reference for admissibility arguments in US courts.
- Issuing body
- Society of Automotive Engineers
- Domain
- Traffic-accident reconstruction
- Methods covered
- Momentum, skid, crush-energy
- Role in court
- Reference for admissibility arguments
Common questions
Why does a court care whether a reconstruction follows an SAE reference?+
Admissibility standards such as Daubert or Frye ask whether a method is generally accepted in the relevant scientific community, and citing a recognised SAE paper or standard gives a reconstructionist a documented basis for that acceptance rather than relying on an ad hoc technique.
What is the difference between the momentum and crush-energy approaches it covers?+
Momentum methods use pre- and post-impact vehicle paths and masses to solve for impact speeds, while crush-energy methods estimate speed from the amount of permanent vehicle deformation, and reconstructionists often cross-check results from both where the physical evidence allows.
Related terms
- Coefficient of Kinetic Friction (Mu)
- The dimensionless ratio of the sliding friction force to the normal force between a tyre and the road; typically 0.55-0.70 for dry...
- Coefficient of Restitution (E)
- The ratio of the relative velocity of separation to the relative velocity of approach in a collision; e = 0 for perfectly...
- Daubert Standard
- The US federal evidentiary standard (Daubert v. Merrell Dow Pharmaceuticals, 1993) requiring that expert testimony be based on scientifically valid methods with...
- Energy-Equivalent Speed (EES / Delta-V)
- The SAE J2080 metric quantifying the kinetic energy absorbed by vehicle crush deformation, expressed as the speed change equivalent; used in the...
- Event Data Recorder (EDR)
- An onboard module that records pre-crash vehicle kinematics (speed, throttle, brake, steering) in the seconds before airbag deployment; governed by SAE J1698...
- Head-Throw Distance (HTD)
- The horizontal distance from the vehicle's front bumper contact zone to the final rest position of the pedestrian's head; used in the...
- IRTE
- Institute of Road Traffic Engineers (UK); publishes the Forensic Collision Investigation manual that governs police and expert-witness reconstruction methodology in England and...
- Momentum Conservation
- In the absence of external horizontal impulses, the total linear momentum of a two-vehicle collision system (sum of mass times velocity for...
- PC-Crash
- Accident reconstruction simulation software (Steffan and Moser, Austria) that models vehicle dynamics, pedestrian multibody kinematics, and collision geometry; validated against crash-test data...
- Skid-Mark Formula
- v = sqrt(2 mu g d), where v is the pre-skid speed (m/s), mu is the coefficient of kinetic friction between tyre...
- Yaw Mark
- A curved, striated tyre impression produced when a vehicle slides at an angle to its direction of travel during a steered or...