Energy-Equivalent Speed (EES / Delta-V)
Definition
The SAE J2080 metric quantifying the kinetic energy absorbed by vehicle crush deformation, expressed as the speed change equivalent; used in the Energy-Balance Method to account for crush energy dissipation in reconstruction.
- Standard
- SAE J2080
- Method context
- Used within the Energy-Balance Method
- Quantifies
- Kinetic energy absorbed by crush deformation
- Expressed as
- An equivalent speed change
Common questions
Why do reconstruction reports pair EES with delta-V instead of using one figure?+
EES describes the energy absorbed by structural crush on a single vehicle, while delta-V describes the change in that vehicle's velocity over the whole impact, including the part that goes into rotation and restitution rather than deformation. The two agree only in specific collision geometries, so both are reported to avoid overstating severity from crush alone.
What limits the accuracy of an SAE J2080 energy-balance calculation?+
The method depends on stiffness coefficients measured for that vehicle class in prior crash tests, so an unusual structure, aftermarket modification, or a vehicle outside the tested database weakens the result and should be flagged with a wider uncertainty range.
Is EES/delta-V from crush analysis enough on its own to prove impact speed in court?+
No. It is normally corroborated with independent evidence such as skid marks, event data recorder output, or witness and scene evidence, since crush-based energy methods carry inherent uncertainty from stiffness assumptions.
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