Low velocity car-to-bus test impacts

Accident Reconstruction Journal 1996; 8(5): 44-56

The process of critical appraisal of published material allows the practitioner to determine the validity of a study and to make a judgment as to its applicability to real world situations. Many studies of this type have been criticized in terms of small sample size, unrepresentative crash conditions, incomplete or inaccurate quotation, selection bias and inadequate follow-up.

SUMMARY

This paper is now ten years old but it is still cited in cases concerning collisions between cars and buses. Such incidents may involve many claimants; including the occupants of a bus struck by a car, typically in a rear-end crash. In this study a 12,020kg bus with reinforced steel bumper was struck in the rear by one of three vehicles; a 1987 Chevrolet Blazer (1700kg), a 1992 Dodge Spirit (1270kg) and a 1992 Plymouth Sundance (1200kg) in a total of 18 (17 rear-end) collisions. The vehicles were equipped with devices to measure velocity change and peak acceleration. Three to fifteen unrestrained bus passengers, mostly adult males, apparently avoided injury in collisions causing a change of velocity (Delta V) of 3.46-17.67 for the bullet vehicles and 0.18-1.91kph for the bus. The subjects reported no more than a slight rocking movement of the head and upper torso, and none reported any symptoms after the event, even with repeated exposures. Meanwhile the driver of the bullet vehicles, a 41 year-old male, complained of headache and neck stiffness lasting 48 hours. The authors concluded that the substantial weight difference of the involved vehicles limited the velocity change and peak accelerations experienced by the bus passengers, and prevented harm at impact speeds below that which would be expected to cause serious or fatal injury in the car’s occupants.

CRITICAL APPRAISAL

In the present study the maximum number of staged collisions was eighteen, with only seventeen involving the rear-end vector. No attempt was made to determine the injury risk to any individual. There was no clinical or radiological examination of any of the subjects and no physician or surgeon was involved in the assessments. To apply the findings to a particular claimant one would have to match the claimant to the experimental subjects in terms of age, gender, past medical history, position in the vehicle, presence of restraining devices etc.

The study involved a maximum of fifteen subjects per collision, sometimes as few as three. Some subjects were seated and some were standing in the aisle. None was restrained. There were no children, no females and no elderly persons.The subjects were not all seated and those who were did not have seat belts.

Sometimes the bus had its brakes applied and sometimes not. All subjects were aware of an impending crash-although they could not see the approaching car. Of seventeen rear-end crashes, an uncertain number were offset while others were more central. The collisions caused by the Chevrolet involved bumper to bumper contact whilst those caused by the other vehicles involved a degree of under-riding of the bullet car’s bumper versus the bus bumper. The relative height of the bumpers is known to influence energy transfer and injury risk.

There are no details on follow-up, save for the comment that subjects did not experience symptoms. No details are provided as to what allowance was made for the frequent occurrence of delayed onset of symptoms, often up to five days after a rear end collision.

The authors’ affiliations are important in any critical appraisal. In the present case the authors are ‘reconstructionists’ with North-Eastern Collision Analysis in Rochester, NH. This body provides accident reconstruction services to law enforcement agencies and insurers, specifically relating to suspected insurance fraud. From their own website (http://northeastcollision.com) the following provides an insight into the core business of the organization: By using the principles of accident reconstruction we may be able to assist the investigator by showing that the reported circumstances or the resultant vehicle damage does not correlate with the reported circumstances of the collision.

The source of the article is also relevant. The ARJ is a publication aimed at the reconstructionist community and is replete with advertisements for products and services appropriate to that industry. A professional relationship with companies seeking to mitigate claims does not impugn the investigators’ independence and it does not, of itself, negate their conclusions. However, one would have expected any sources of funding, or potential conflicts of interest, to be declared at the end of the article to allay any concerns over publication bias.

Finally, we are given no information as to the subjects themselves. In many similar studies the subjects have been recruited through newspaper advertisements. Some have presented themselves for repeated experiments for financial gain. Others have been the researchers themselves, co-workers or members of their families. All of these may be tempted under-report any mild symptoms. No details are provided as to the methods used to counteract these influences.

The duties of a doctor are defined by the GMC (http://www.gmc.org/standards/good.htm) and they include not writing or signing any documents which are false or misleading because they omit relevant information. When one cites any paper it is essential to draw attention to the strengths and weaknesses of the study, particularly when the authors themselves refer to areas of uncertainty. The present authors state that care must be taken when estimating delta V in low speed impacts. In low speed collision, external forces such as braking and restitution cannot be ignored. The authors make some attempt to account for these factors and they conclude that, in these terms at least, their staged collisions were representative of real world crashes. However, before one can apply these findings to a particular personal injury case, these (and other) crash-related factors must also be determined for the index crash.

SUMMARY

At first glance this paper looks as though it may assist in the assessment of claimed injury among bus passengers whose vehicle is hit from behind by a car. Quite simply, the paper suggests that injury may not occur and, by extension, any injuries claimed must be fraudulent in these circumstances. However, the paper does not stand up to scrutiny through a process of critical appraisal. The study is industry-based and published in a trade journal. It involves very few (male) subjects in a small number of unrepresentative staged collisions, and it fails to take account of many factors known to influence injury risk. Follow-up was inadequate and did not involve clinical (Eg. Cervical range of motion) or radiological assessment by medically-qualified persons.