Expert Witness Blog
In Accident Reconstruction of Low Speed Impacts, accident reconstruction and automotive engineering expert witness writes:
Even if high speed barrier crash tests could be validly generalized to low-speed crashes with moving cars, they cannot help predict the energy transferred in any one crash because vehicles differ considerably in their ability to absorb certain impacts without showing damage. In this case, that variability would apply to the damage to the bullet’s front bumper and target’s rear bumper.
One example of the variability between vehicles is that older vehicles generally have stronger bumpers and can absorb greater impacts while showing less damage than newer cars because newer cars are frequently equipped with bumpers where style dominates over function.
A second example of bumper variability is between individual cars regardless of vintage. Bumpers vary greatly a lot in terms of their components and performance, even among cars of similar size and style. In 1982 the federal government scaled back the impact test requirements from requiring bumpers to withstand all but minor cosmetic damage in a 5 mph. impact to requiring bumpers withstand all but minor cosmetic damage in a 2.5 mph impact. Thus, while crash tests are useful in extracting generalities about the biomechanical processes of a collision, they cannot reliably predict the energy transferred in a particular collision.