minimal damage

Is Acceleration a Valid Proxy for Injury Risk in Minimal Damage Traffic Crashes? A Comparative Review of Volunteer, ADL and Real-World Studies

Goal of the Study?

In this study 1, the authors evaluate the scientific validity of using the biomechanical approach to assess injury causation from minimal damage traffic crashes.


Why are they doing this study?

A major point of contention in civil litigation cases following traffic injury claims is related to causation. Claimants generally rely on their doctor’s expertise to explain the cause of a persistent injury following a crash. In contrast, insurers often rely on a biomechanical approach as a basis for denying any link between the crash and ongoing injuries. The theoretical basis of the biomechanical approach is that the risk of injury from a crash is the same as the forces of activities of daily living (ADLs). However, the authors argue that the literature does not support this approach. Findings of large epidemiologic studies indicate that the injury rate is significantly greater in minimal and no damage crashes than ADLs.


What was done?

For this review, the authors included literature from three categories: volunteer rear-impact crash testing studies, ADL studies that describe linear and angular head acceleration for various ADL activities, and observational studies of real-world impacts. They compared the occupant accelerations of minimal or no damage (3-11kph speed change or delta-V) rear-impact crash tests to the accelerations described in 6 of the most commonly reported ADLs in the reviewed studies. The injury risk observed in real-world crashes compared to the results of the pooled crash test and ADL analyses, controlling for delta-V and adjusting for test subject age and sex. 


What did they find?

The authors argue that the biomechanical injury causation approach is scientifically invalid. Research illustrates that both crash testing results and epidemiologic data from real-world rear crashes show that there is a substantial risk of injury even at the lowest levels of impact severity. This stands in contrast to ADLs that have virtually no risk. They found that the average acceleration forces of the head during rear-impact crash tests were several times greater than average forces experienced during ADLs. Moreover, the injury risk of real-world minimal damage rear-impact crashes was estimated to be at least 2000 times greater than for any ADL. For example, research has indicated a 54% risk of any cervical spine injury and a 6% risk of any injury lasting for more than 6 months in an 11km/h rear impact delta-V crash. For this reason, they argue that the basis underlying the biomechanical injury causation approach, which uses occupant acceleration as a proxy for injury risk, vastly underestimates the actual risk of such crashes and should not be used in practice. 


Why do these findings matter?

The results of this review challenge the use of the biomechanical approach and illustrate how it underestimates the risk of minimal damage crashes on those involved.