Crash Study: Low Speed Impact and Occupant Injury
By Richard H. Adler
December 13, 1991
More and more scientific studies are demonstrating that while low speed impact may result in minor property damage, they can cause major injury.
Recently, Dr. Francis Navin, Professor of Civil Engineering, and Dr. P. Romilly, Professor of Mechanical Engineering at the University of British Columbia, simulated low speed rear-end impacts to assess vehicle damage and occupant injury. The investigators hoped to answer the question “Are the numerous whiplash injuries reported by victims of low speed rear-end impacts actually genuine?” The results of this experiment indicate that vehicles can withstand a 15 km/h (9.3 mph) impact without structural damage, but that the occupants in the vehicle accelerate faster than the impacted vehicle. This magnification of acceleration creates the environment in which injuries occur.
Drs. Navin and Romilly set up a simulated experiment in which a heavy pendulum was swung at speeds between 8 and 20 km/h (4.96 to 12.4 mph), striking the rear bumper of a Volkswagen Rabbit carrying bolted anatomical crash dummies. Chains were fastened loosely between the vehicle and the floor to prevent excessive movement after the test. The parking brake was engaged and the vehicle was placed in gear. The roadway surface was level and dry.
For impact speeds below 15 km/h, there was insignificant damage to the vehicle. Stated differently, the amount of energy absorbed during this process was minimal when compared to the total elastic energy. Also, the data revealed that a substantial time lag (50 ms) existed between the vehicle and the occupant motion. The researchers were able to demonstrate the physics principle known as “magnification of acceleration”:
This time lag is significant as the vehicle had achieved its final velocity before the occupant started to move. The occupant encounters higher speeds…attempts to “catch up” with the car…the occupant(s) accelerated forward to a velocity higher than the car velocity…. It is important to recognize that the shoulder is rebounding before the head. This relative movement of the head to the shoulder during the rebound is the likely cause of the neck injuries as this is a point at which dynamic loading of the neck will be at a maximum.
This study presents strong and convincing evidence that vehicles which do not sustain damage in low-speed impacts can produce correspondingly higher dynamic loadings to their occupants than those vehicles which plastically deform under the same or possibly more severe impact conditions. During a collision, the vehicle structure deforms, converting the system’s kinetic energy into sound, thermal, and strain energies. The rate of “deformation” defines the vehicle’s “plastic” characteristics while the amount of “recoverable deformation” is a function of its elastic properties. For example, at higher impact speeds, very little elastic recovery occurs and the vehicle generally behaves as a plastic body. At low impact speeds, “plastic” characteristics may be absent, allowing more of the total impact energy to recover in elastic rebound.
Of most significance to the health care provider, this study demonstrates that patients who have been in rear-end collisions and experienced little damage to their vehicle can have legitimate complaints of injury. To understand the acceleration forces and provide proper treatment for injuries they may cause, the health care provider and insurance representative must look beyond false notions that “no property damage means no or little injury.”
Additionally, the provider needs to take into account various physical factors involved in an accident, such as the principal of magnification of acceleration, road surface conditions, velocity of vehicle, whether the struck vehicle had been braking, the distance the vehicles moved after impact, respective size and weight of the vehicles, position of head restraints, age of the injured party, whether the head was rotated, etc.
As you may know, our law firm represents individuals with personal injury claims. We welcome and appreciate the referral of your patient to consult with us on medical-legal-insurance issues. Our initial consultations are without cost to your patient. If you or your patient need advice or would just like some questions answered, we’ll be glad to help. Simply give us a call.
Very truly yours,
ADLER GIERSCH, P.S.
Richard H. Adler
Attorney at Law