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Cause and Contributing Factors in Traffic Accidents

By James O. Harris Email:

When the facts are against you, argue the law;
When the law is against you, argue the facts.

The above is often quoted to aspiring attorneys. To successfully argue the facts of a case, the advocate must understand their contribution to the proximate cause of an issue and the factors leading to a result. This is one reason there are expert witnesses. Few trials would be complete without expert testimony.

The ultimate goal of a traffic accident investigation or reconstruction is to determine the events of the accident, or what caused the accident. There are many publications available on the subject of cause as cause is the heart of the issue at trial. The subject matter can be complex since there are so many circumstances and factors that must be considered in a cause analysis. There is also the matter of what does "cause" mean?

One pitfall a reconstructionist, or an attorney, faces is defining "cause." As most of the reconstructionist's work involves the legal profession, a common understanding of the legal term will be useful to prevent confusion.

Cause in law is different from cause in the rest of the world. In the eyes of the courts, cause is an issue of policy and not an instrument of factual analysis. The issue for the court is whether, as a policy decision, a defendant should be held liable for injuries or damages. In a traffic accident case, the resolution of that issue depends on whether the crash was a foreseeable result of a defendant's negligence or willful act.

This sounds contrary to that which is taught to police officers, traffic homicide investigators and accident reconstructionists. The work of the accident investigator is preliminary to the analysis performed by the jury. The jury is bound to consider the evidence and will consider the quality and completeness of the analyst's presentation in coming to a conclusion. Put another way, the juror is not constrained to the same principles of factual analysis as is the investigator.

Many jurisdictions hold that any event that was a substantial factor in causing a harmful event is a legally relevant proximate cause of the event even if other things were also substantial factors and therefore concurring proximate causes of that event. This does not mean a law violation must be construed as a causative factor in an accident. For example, a vehicle's registration may have expired but this would not be relative to the vehicle being involved in a collision although it is a violation. Many traffic laws exist solely to govern the safe movement of traffic on the highways; stop signs, lane division, speed limits, etc., and may concur with an accident factor that existed. For the police officer, it is convenient to match a law violation with a "cause" but this practice often results in errors as it tends to ignore other existing factors that may have been present and were equally contributing to an accident.

A common law violation that is considered a modifier of the human factor is intoxication. Assume a vehicle is stopped at a stop sign. The driver is legally intoxicated. His car is struck in the rear end by another vehicle. The fact that the driver of the lead vehicle is intoxicated is not a factor in this accident but the law violation is present. His performance did not contribute to the event. When determining intoxication as a factor in an accident, the effect of the level of intoxication in the human performance factor needs to be quantified. For example, if a driver was not intoxicated, would the accident still have occurred?

Outside the courtroom and in factual analysis, cause is whatever is required to produce a result. A case normally consists of a combination of factors, circumstances or conditions that must be present to produce the result. Consider a cigarette lighter. For a flame to be produced, there must be fuel, a flint, a striking surface this is free of moisture and someone to actuate the mechanism. Take out any of these circumstances and the lighter will not produce a flame. Not only must these circumstances be present, they must be present simultaneously. In this example, it is a simple matter to find one circumstance that must be present to produce the result, such as the fuel, but in other situations the factors may be difficult to identify.

When circumstances or conditions exist simultaneously, the degree of each condition may be important. Consider two drivers, Smith and Jones. Smith, with better visual acuity, can see better in dim light than Jones. Driving along a dark country road, without headlights, neither driver can see a pedestrian walking along the side of the road. With high beam headlights, both Smith and Jones can see the pedestrian. With low beam headlights, Smith can see the pedestrian but not Jones. High beams allow Jones, even with his poorer visual capacity, to see the pedestrian as can Smith. But Jones cannot see as well as Smith under the same circumstances even though the environmental conditions were identical. An analysis of an accident involving Jones and the pedestrian would include trying to determine whether it was due to poor visual acuity or insufficient lighting conditions. If three or more conditions interrelate, the evaluation of the circumstances becomes considerably more complex.

Conditions and events are closely interrelated when considering accident factors. Some may be obvious and others difficult to determine. If a large truck is involved in an accident and the fuel tank is ruptured, the cause of the rupture and resulting fuel spill, is readily determined. If the fuel was to ignite, the cause of the ignition may be indeterminate but subject to speculation.

A "factor" is a circumstance contributing to a result. Without this factor, the result would not exist but the factor alone is an element that, by itself, cannot produce the result. The term "contributing factor" is meaningless if this definition is accepted. A factor must be contributing if it is present otherwise it is not a factor. The term "primary factor" is sometimes used by experts to indicate a factor that was strong in its contribution to the accident. This is misleading as there can be no one factor more important than any other if all factors must have been present to produce a result. No factor can be secondary, or less important than another if all are required for the result. Like the links of a chain, all must be present and none is more or less necessary than the other.

Consider a road with a sharp curve. One year, 10,000 cars safely negotiate the curve. During the same year, 50 cars failed to negotiate the curve and crashed. What was the cause of the accidents? If it is accepted that the sharp curve was the cause, then all the cars traveling on this road would have had an accident. It may well be a factor, but certainly not the sole circumstance in existence that precipitated the accidents. A combination of factors, speed, driver capability, vehicle condition and environmental conditions all come into play.

In a two car head-on collision, multiple factors again come into focus. Why was one driver left of center? Was it a problem of perception? Or attitude? Why did the other driver not take evasive action? Did a passenger not warn the driver of the impending hazard? Is there road design defect? A failure to properly mark, sign or maintain the road? Obviously, many questions are not addressed and will not be answered by a police officer filling in blocks on a standard accident report form.

Actors fall into three primary areas: road, vehicle and human. Each area is subject to a variety of modifiers. For instance, road factors include, but are not limited to lighting, view obstructions, recognizability, signs, signals, surface character, dimensions and protective devices. All factors are subject to modification by outside influences such as the road surface that becomes slick from rainfall. Modifying each of the listed road factors are weather, lighting, roadside devices, activities, surface deposits, damage, deterioration and age.

For vehicles, factors include equipment condition, view obstructions, distractions, instruments, signaling devices, control sensation, comfort, automatic controls and devices, weight, performance, dimensions and stability. Vehicle speed, as a factor, must exist. If neither vehicle had any speed, there could not have been a collision.

Human factors are without doubt the most complex and difficult to isolate as they are almost all very temporary in nature. What existed at the time of the accident may not exist moments later. Consider sensory capabilities, knowledge, judgment, attitude, alertness, health, driving skill, age, customs, habits, weight, strength and freedom of movement. Of these, the emotional factors are the greatest variable attributes and the most difficult to identify. They are also subject to the most modification with the least remaining evidence.

Remote condition factors may be considered when dealing with cause analysis although they are seldom of significance to the investigator on a single accident case. Remote condition factors may involve a changing cultural climate in which the factors and their modifiers form. This includes moral influences, religion, beliefs, legal influence and values on vehicle designers, highway engineers, drivers and pedestrians.

In most reconstructions preformed for civil litigation, collision avoidance is an issue. Much of this analysis falls under a category of predisposing circumstances. Some of these circumstances can be controlled by the individual. In small amounts, alcohol in the bloodstream may have little effect on a driver's capabilities. In larger quantities, the effect can be dramatic and greatly increase the chances of an accident. A driver may be exposed to a predisposing circumstance, such as consuming moderate amounts of alcohol before driving for many years and never have an accident. It is only when this circumstance is combined with other circumstances that the full effect of the predisposing circumstance becomes evident. Other predisposing circumstances, like driving in a rainstorm, can be avoided by trip planning.

Determining all the factors that were present in any single accident would be a monumental undertaking. With human foibles, none will ever be complete or accurate. There are simply too many factors, modifiers and circumstances present that may have disappeared long before the investigator becomes involved. Other circumstances may simply never be revealed, or realized, by the parties involved. The examination of many accidents at one location may reveal a single, unique circumstance common to all accidents there. This is useful in isolating a factor not readily observable in a single case.

The essential test for proximate cause is the accident must be the natural and probable result of a negligent act or omission and be of such a character as an ordinarily prudent person ought to have foreseen it as likely to occur as a result of the action. It is not essential that the person charged with the negligence should have foreseen the precise injury from his action.

This definition makes the work of the accident analyst and advocate easier in that not all the factors present in an accident may be sufficiently relevant to the cause for consideration. Mere presence is insufficient, it must have in some significant way contributed to the result. As such, there are several factors that are routinely identified as being substantially contributing and others are accepted or implied as being present and normally expected. In a case where a vehicle falls or flips, gravity is a factor and its existence is accepted. This does not relieve the analyst of the responsibility of being aware of the presence of additional factors because in any case any one of them may be critical in determining proximate cause.

With a good understanding of the relationships of accident factors, circumstances and modifiers, and sufficient data, an accident can be analyzed, causation determined and the conclusions effectively presented.