From McHenry Accident Reconstruction:
- "Confusion in the interpretation of damage in actual accidents can be created by the use of the term Barrier Equivalent Velocity as opposed to Barrier Impact Velocity in the specification of corresponding test conditions. Such confusion comes from the following definition (e.g., Reference ) of the Barrier Equivalent Velocity (BEV):
BEV is “the equivalent impact velocity of a vehicle into a fixed, rigid barrier that would result in the same magnitude of crush as observed on a subject vehicle under analysis.”
Clearly, when a vehicle with a stiff front structure collides with the softer rear of another vehicle, the magnitude of crush on the striking vehicle will be less than that in a corresponding barrier crash with the same impact speed-change. Thus, a simplistic crush comparison on the striking vehicle, using the above BEV definition and the specified BEV values for air bag deployment, will generally lead to the conclusion that the BEV was below that specified for the airbag deployment threshold. Note that this confusion could be overcome by either (a) the definition of deployment thresholds in terms of Barrier Impact Velocity rather than BEV, or (b) a more proper definition of BEV as meaning “that portion of the impact speed-change that precedes the achievement of a common velocity.”
The concept of assessing impact severity by relating the damage sustained in a collision to that which the same vehicle sustains in an experimental barrier impact test (e.g., the Barrier Equivalent Velocity (BEV) concept) was first described by Mackay in 1968 (Ref. ). When the two vehicles involved in a car-to-car collision have essentially similar deformation and weight characteristics, such a BEV method of assessing impact severity can be reasonably reliable for use in statistical studies. However, if the vehicles have dissimilar characteristics, the BEV ratings can be considerably in error as a measure of impact severity. For example, if a heavy soft car collides with a light stiff car, it is possible for the stiffer car to experience a substantial change in velocity with no appreciable damage (Ref. , ).
A barrier impact velocity of X MPH produces an impact speed-change, Delta-V, of X MPH plus the rebound velocity, if any. If the barrier is replaced by a standing, “mirror-image” vehicle, the same extent of damage and the same impact speed-change, Delta-V, as occurred in the barrier impact will be produced by a closing velocity twice as large as the barrier impact velocity (i.e., a closing velocity of 2X). The interpretation of damage in actual collisions in terms of BEV, or Delta-V, requires proper consideration of the mass and stiffness ratios of the collision partners and of the effects of any collision offset (e.g., 4)".
- 1. Kerkhoff, J.F., Husher, S.E., et al, “ An Investigation into Vehicle Frontal Impact Stiffness, BEV and Repeated Testing for Reconstruction”, Society of Automotive Engineers Paper No. 930899.
2. Ashton, S.J., Hardy, J.L.G., Mackay, G.M., “The Use of the Vehicle Deformation Index and Collision Speed Assessments”, Proceedings of the International Accident Investigation Workshop, Pilot Study on Road Safety, NATO, Brussels, Belgium, June 28-29, 1973.
3. Hight, P.V., Lent-Koop, D.B., Hight, R.A., “Barrier Equivalent Velocity, Delta-V, and CRASH3 Stiffness in Automobile Collisions”, Society of Automotive Engineers Paper No. 850437.
4 Knipling, R.R., Kurke, D.S., “NASS Field Techniques – Volume IV – CRASH MEASUREMENTS”, US Department of Transportation, National Accident Sampling System,