Low Speed Crashes
and Missed Vehicle Damage
Standards to Demand in a Vehicle Inspection
By: Patrick Sundby, Accident Investigator
Specializing in Low Speed and Catastrophic Crashes
Mark Studin DC, FASBE(C), DAAPM, DAAMLP
One of the most common problems with low speed collisions is determining the extent of the damage. The common real world practice is to visually examine the exterior of the vehicle and document any damage. The problem with this is not knowing the extent of the damage behind the exterior panels. Very few cases have had through and complete vehicle examination. The question is why?
The crash Reconstructionist has a tedious job ahead of him when facing a collision with what appears to be minimal damage at first glance. Happer et al (2003) acknowledges different vehicles will have different damage, or appearance of damage, at the same speed due to different designs. The goal of the paper was to provide a sound method for determining the severity of a collision. Happer et al (2003) also states the physical evidence remaining after the impact must be reviewed and this process begins with dividing bumpers into three categories. In this writing we will focus on the second one, reinforcement beams with a polymer absorber. These bumpers are categorized as having a metal reinforcement beam with a polymer absorber behind a plastic or urethane cover; this is the bumper to focus on as the vast majority of the vehicles on the road today are constructed in this manner.
Below is a picture of one such polymer structure. In this instance a vehicle struck a guardrail (during a training event) in a glancing motion and the polymer structure was pushed out of the bumper cover.
In the above photograph the damage is obvious, what we need to focus on are the collisions where damage appears minimal. The purpose of the polymer structure is to crush under a predetermined load to reduce the damage to a vehicle during lower speed collisions. This structure eliminates or reduces the damage to structural parts and thus will reduce the cost of repair as well. The energy it takes to deform the polymer structure also reduces the likelihood of injury to the occupant – IF it deforms. When the polymer structure doesn’t deform what are the consequences? Consider the photograph below:
The vehicle in the photograph was the striking vehicle in a rear end collision. The bulge & paint scraps in the bumper cover, the misalignment of the front fascia to the hood and fender (next to the headlight), and a small crack in the edge of the fascia near the grill are all external signs of damage. In this case, the vehicle was deemed to have “minor” damage but no further structural analysis was completed. How can one be sure the damage is limited to just what we see?
Let’s take a minute and draw a comparison. Dr. Studin has often spoke of strain/sprain. As a quick recap, there are three levels, primary stretches the tissue & fibers, and secondary begins to tear the tissue & fibers, and tertiary is a complete tearing of the tissue and fibers. When a patient has a complaint of pain and there are no outwards signs of trauma, i.e.: no scrapes, bruising, or other wounds some form of medical imaging is ordered. The imaging is ordered to see inside of the patient and determine if there is any internal injury. Trauma to a disc in the cervical spine (neck) is an example of an injury which would not be expected to show up on any external physical exam but should be easily seen in a good medical imaging process and with correct image reading or interpretation.
The concept of examining a patient completely to determine the source of the problem is the same template which should be applied to a vehicle inspection. A complete inspection demands measuring all the structural components against known factory specifications, this process could entail the removal of the bumper cover, grill, headlights, and other parts to ensure accuracy. Further, as time passes secondary systems can elude to undisclosed damage. As an example, if the geometry of the suspension changed due to a collision the alignment could be off resulting in uneven tire wear. It would take some time for the wear patterns in the tires to change.
The concern for this level of detail can be summarized by saying any energy which is absorbed by the vehicle, but not accounted for, will reduce the final calculated speeds. If you want to be sure about the results, you need to be sure about the facts and must have all the internal protective structures analyzed, not just the “skin of the car.” A perfect understructure can indicate significant energy transferences to the occupant, where “crushed” understructures can mean the car absorbed or deflected the energy and protected the occupant.
Not knowing is leaving the final answer to rhetoric vs. the truth, with physics to back it up.
Happer, A., Hughes, M., Peck, M., and Boehme, S., "Practical Analysis Methodology for Low Speed Vehicle Collisions Involving Vehicles with Modern Bumper Systems," SAE Technical Paper 2003-01-0492, 2003, doi:10.4271/2003-01-0492.