Analysis of Real World Car Crashes
There is no doubt that tests of rear-end impacts in the laboratory provide valuable information into the nature of whiplash injuries. It is also true that medical studies that investigate patient symptoms after a rear-end collision can help us understand the natural course of the whiplash syndrome and devise effective treatments. A new study1 attempts to combine both disciplines by examining both the engineering and the symptomatic aspects of rear-end collisions. Furthermore, the author specifically addresses important factors such as occupant awareness, gender, predisposition to injury, and head orientation.
The author begins his paper with a concise summary of the whiplash problem:
"It is well documented that injuries occur in rear impacts. What is more interesting is the frequency of their occurrence and their repeatability. Emori and Horiguchi2 reported that in Japan over 40% of the total injuries in automobile accidents are 'whiplash' injuries. Similar studies in the United States have also shown surprisingly high rates of injury in rear impacts. One study by the NTSB3 showed injury rates as high as 100 percent for restrained drivers and occupants involved in tow-away rear collisions. Another study4 has demonstrated that while occupants are half as likely to be killed in rear impacts, they are almost twice as likely to be injured, when compared to frontal and side impacts."
The author investigated 72 rear impact collisions that had occurred in the real world. The subjects included a mix of people with and without injury, and with and without litigation. All collisions were from one to three years old when they were reconstructed by the author. The data for analysis was compiled by a questionnaire that the vehicle occupant answered, medical records, and police reports. For each collision, the author calculated an approximate DV (Delta V), or velocity change, that was experienced by the struck vehicle.
After analyzing the data, the author compiled a chart showing the relationship between occupant awareness of the impending collision and the Delta V.
Delta V |
Aware |
Number |
Neck |
Back |
Head |
Other |
0 - 5 |
Y |
1 |
0 |
0 |
0 |
0 |
5 - 10 |
Y |
0 |
0 |
0 |
0 |
0 |
10 - 15 |
Y |
4 |
0 |
1 |
0 |
0 |
15 - 20 |
Y |
5 |
1 |
3 |
0 |
1 |
20 - 25 |
Y |
2 |
1 |
1 |
0 |
0 |
25 - 30 |
Y |
1 |
0 |
0 |
0 |
0 |
30 - 35 |
Y |
0 |
0 |
0 |
0 |
0 |
Over 35 |
Y |
1 |
1 |
1 |
1 |
0 |
"This table clearly shows a direct relationship between awareness and neck complaint rates. The relationship was virtually one-to-one in the cases studies for this paper...[This] relationship between awareness and complaints was further demonstrated in cases where a struck vehicle had multiple occupants but not everyone had reported complaints. In the study, numerous examples were found where the driver of a vehicle saw the impending impact, braced and did not report any complaints. In the same collision, unaware passengers did report complaints."
The study also provides some new insights into some other areas of interest in whiplash injuries: mild traumatic brain injury, TMJ pain, shoulder complaints, and head position.
The author examined the issue of direct head impact in pickup truck occupants:
"Due to extensive testing in this area, we know that the struck vehicle, in a rear impact, reaches final velocity before the occupant begins to move. As the head moves rearward relative to the body, it can strike the headrest or back of the cab at a velocity equal to the vehicle's change in velocity. In pickup trucks, this aspect combined with the ramping demonstrated by numerous researchers, can result in the occupant's head striking the metal cab at high velocity, resulting in high levels of acceleration. The calculated levels of acceleration, in this situation, easily reached the magnitude where closed head injuries can be expected. It is clear that the use of greater padding in the back of truck cabs would result in a significant reduction of acceleration levels and, therefore, expected injuries."
TMJ symptoms were also commonly reported among occupants:
"In the sample there were thirteen cases of TMJ dysfunction reported. All of the cases were associated with unaware occupants being struck from behind. The probable time of injury appears to be during the initial rearward motion (extension), as the head and jaw are subjected to high acceleration levels. It is worth noting, that of the 13 occupants with TMJ complaints, only one was a man. It is well known that women are more susceptible to TMJ dysfunction than are men. Therefore, it is possible that the rear impact provided the extra force necessary to initiate the TMJ in women who were already predisposed to it."
Furthermore, seat belts seem to be related to the frequency of TMJ symptoms: "This class of complaints, which included TMJ complaints and shoulder complaints, was over represented in the seat belt wearing population. However, due to the small size of the sample, more data is required."
In regard to shoulder pain, the author writes, "The leading causes of shoulder complaints, in rear impacts, appear to be the direct loading from the seat belt and differential loading from the seat back. As an example of the former, numerous left shoulder complaints are seen in drivers, while right shoulder complaints occur in passengers. Often this complaint is overlooked due to other more debilitating complaints in the neck or back."
Finally, the author addressed the issue of occupant head position during impact. "The onset of complaints occurs at a lower [delta V], and with greater severity, if the occupant's head is outside the normal plane of the head/neck complex [i.e., looking straight forward] at the time of impact. It is informative to note that of the two aware occupants who experienced neck complaints, one had his head turned."
- Smith JJ. An analysis of 72 real world impacts – an initial investigation into injury and complaint factors. Society of Automotive Engineers International Congress and Exposition, March 1-4, 1999;SAE 1999-01-0640.
- Emori RI, Horiguchi J. Whiplash in low speed vehicle collisions. 1990 SAE 900542.
- NTSB Safety Study (SS) 88/03, Performance of lap/shoulder belts in 167 motor vehicle crashes, 1988.
- Navin & Romilly. An investigation into vehicle and occupant response subject to low speed rear impacts. Proceedings of the Multidisciplinary Road Safety Conference VI, June 1989.
