An occupant is ejected from a vehicle and it is claimed that the ejection was the cause of the resultant fatal head injuries. This is the latest conclusion reached from a collision yesterday night in Toronto when a relatively minor intersection collision resulted in fatal injuries to one of the drivers.

Remarks were made that, had the driver been wearing a seat-belt, he would have survived.

Statistics along with the reconstruction of vast numbers of collisions over the past 4 decades confirm that seat-belts have been greatly successful in reducing the severity of injury and preventing numerous deaths. However, when speaking about the specifics of individual collisions the public ought to understand that what is officially reported is not always the factual truth. Not that intentional lies are spread, but that sometimes the information passed onto the public is simply incorrect. With respect to the fatal head injuries, the correct source is not always found.

Intersection collisions such as the one described above occur within patterns and the process of their investigation/reconstruction needs to follow standard procedures. Firstly, the paths of the vehicles leading to and from impact need to documented via the physical evidence that will exist on the road. Once those paths are defined the next step is to match the vehicles to themselves using similar procedures of matching the physical evidence residing in their mutual areas of direct contact. Once this second step is achieved it is then possible to explore the motion of an occupant’s body with respect to the vehicle interior.

In recent years the availability of event data recorders (“black box”) has helped in providing objective data for several seconds before, during and sometimes for several seconds after impact. While this additional precision is helpful it needs to be interpreted with caution. While reliable in a vast majority of instances, EDR data can contain “quirks” that, if not detected, can lead investigations astray. This is why specialized training in necessary to inform investigators of those instances where false data may develop.

With respect to the occupant’s motion within a vehicle during an impact, seat-belt use confines that motion to a large degree as long as the occupant remains restrained. Yet improper seat belt usage or malfunctions of the restraint system can occur. When over 95% of the driving public uses seat belts this should lead investigators to be cautious whenever evidence appears to show non-usage because of the rarity of that occurrence. While EDR data will often indicate whether a seat belt switch is closed, generally indicating seat belt usage, experience has demonstrated that the value of this parameter is not always accurate.

Seat belt usage and the source of occupant injury need to be determined by examining three areas of evidence: 1.) the pattern of injury to the occupant, 2.) the location and character of visible contacts to the vehicle interior, and 3.) the characteristics and locations of visible loading marks on the restraint system. It requires experience to understand what these three areas of evidence reveal.

In the situation of the collision noted above, frontal damage on one vehicle is often associated with side damage on the collision partner. For the vehicle with frontal damage there is an understandably large amount of rotation that is initiated because of the relatively long distance between point of application of the collision force and the vehicle’s centre-of-gravity. Because of this rotation the direction of occupant motion can change drastically between initial and final paths with respect to the interior. While it was concluded that the fatally injured occupant in the present case was ejected via the passenger’s side window, significant head contact can be made to stiff portions of the vehicle interior, such as roof pillars, that can cause a major injury before the ejection occurs.

Furthermore, rotations during intersection collisions often result in the slapping together of the near sides of the collision partners. In this instance, as this occupant is being ejected through the side window, the opposing vehicle may be located within the perimeter of the window resulting in the occupant making head contact with the exterior of that opposing vehicle before final ejection is achieved.

Yes it is true  that fatal head injuries to ejected occupants occur from striking the exterior road environment such as the road surface or other objects on the roadside. However it is important to understand the complexity of the issue and be able to match the injury to the correct source. This may appear to be a moot point to many readers of these tragic news stories but correct identification of the source of a critical injury affects the safety of all of us because it changes the direction of efforts and funds toward the prevention of future tragedies.