It is rare when we can compliment Ontario police forces in being transparent and useful toward educating the public on road safety. The OPP in Ontario have been an exception, at least with respect to providing photos of serious collisions in their jurisdictions. Most recently three photos were shared on the OPP Twitter account showing the results of a two-vehicle impact involving a BMW. While no other information was provided, the photos of the BMW enable us to comment on the very important issue of serious rear-end impacts occurring on Ontario’s 400-series expressways and higher-speed unban arterials.
The photo above shows the damage caused to the BMW and this side view is helpful in demonstrating the extent and location of the damage. Looking the distance between the two wheel hubs along with the lack of damage along the lower sill it is possible to detect that there was not a great deal of energy dissipation taking place at this lower level. In other words there is essentially no crush exhibited at this lower level. This would not occur in a typical collision with another light vehicle or barrier.
There is also evidence of damage and crush above the bumper, or what we say “at the grill level”. In discussing the severity of impacts and the “change-in-velocity” it has been historically important to understand that the bumper level is stiffer and the grill level is softer. So when reconstructionists need to estimate the severity of a collision they need to take this difference into consideration. Yet, while there is a lack of crush at the bumper level, the evidence of major deformation at the grill level is an important demonstration that such a condition is dangerous. The normal relationship between “change-in-velocity” and injury does not apply well in this scenario because of the structural intrusion into the occupant space that occurs.
The danger of structural intrusion has been known for decades. It is dangerous because neither seat-belts nor air bags can be fully-effective when the force of a collision is applied to the occupant and the ride-down that is normally afforded by seat-belts and air bags is minimized.
In the assessment of occupant injury it is important to know how much a vehicle slowed down during an impact but the time involved is also important. A vehicle that changes its velocity in 100 milli-seconds is more likely to result in injury than a vehicle that slows down in 300 milli-seconds. With a shorter crash pulse the accelerations (“decelerations”) must be higher, sometimes with dangerous spikes in acceleration (“deceleration). (Note that, technically, there is no such thing as deceleration, there is only positive or negative acceleration).
In studying the crashworthiness of a vehicle it is also important to establish the magnitude of crush, where it is located and how the shape of the vehicle has been changed from its original dimensions. Historically, researchers have believed that all that was important about vehicle damage is the magnitude of crush. No consideration had been taken into where the crush was located or how the shape of the vehicle was changed. That is a regrettable failure that continues to this day. This additional level of detail is difficult to obtain, time-consuming and therefore costly to achieve.
Attempting to determine where the crush is located and how the vehicle’s shape has been changed is difficult as shown in the photo below. Some of the resultant damage is caused by emergency personnel in their attempts to gain access to the injured and removing them to hospital. Was the hood removed by emergency personnel? Was the windshield peeled away to access the driver? Were the doors removed by them? Some of the answers are obvious while some are not.
Fortunately, new tools such as laser scanners can provide an accurate description of the crush and shape of a damaged vehicle. Yet investigators still do not understand how they might use this valuable tool for assessing vehicle crashworthiness. Event Data Recorders (“Black Boxes”) have also been helpful in filling in the details that were previously unavailable or difficult to retrieve with traditional methods or reconstruction.
However, the photo below shows the suspected danger of the incident. While the lower rocker panel below the doors appears undamaged, the dash and steering assembly do not appear to be in their original locations. In cases of structural intrusion much of the destruction comes from the actions of emergency personnel attempting to pry the occupant from the vehicle and so determining the extent of structural intrusion becomes problematic. The analysis still involves a detailed examination of the physical evidence by an experienced investigator who can recognize the difference and characteristics of evidence. Normally such experience is not obtained from attending two-week instruction courses but requires many years of continuous exposure to such evidence.
In all, the OPP have been helpful in providing the above three photos of the damaged BMW. This information helps to show how a serious rear-end impact of a truck causes minimal crush at the bumper level while causing major intrusion at the upper levels of a passenger car’s front end. For those who believe that they can speed and that the availability of modern technology will protect them, this is an example where modern technology is of lessened benefit. It demonstrates how important it is that all vehicles be equipped with reliable, automatic, emergency braking and that we need to deal with the age-old problem of bumper mis-match and under-ride and differences in vehicle heights that cause needless injuries and deaths.