Motor vehicle accident causes

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Vishnu Vardhan Serla M.B.B.S. [2]

Causes[edit | edit source]

A 1985 study by K. Rumar, using British and American crash reports as data, found that 57% of crashes were due solely to driver factors, 27% to combined roadway and driver factors, 6% to combined vehicle and driver factors, 3% solely to roadway factors, 3% to combined roadway, driver, and vehicle factors, 2% solely to vehicle factors and 1% to combined roadway and vehicle factors.^[1]

Human Factors[edit | edit source]

Human factors in vehicle collisions include all factors related to drivers and other road users that may contribute to a collision. Examples include driver behavior, visual and auditory acuity, decision-making ability, and reaction speed.

A 1985 report based on British and American crash data found driver error, intoxication and other human factors contribute wholly or partly to about 93% of crashes.^[1]

An RAC survey of British drivers found that most thought they were better than average drivers; a contradictory result showing overconfidence in their abilities. Nearly all drivers who had been in a crash did not believe themselves to be at fault.^[2] One survey of drivers reported that they thought the key elements of good driving were:^[3]

• Controlling a car including a good awareness of the car's size and capabilities
• Reading and reacting to road conditions, weather, road signs and the environment
• Alertness, reading, and anticipating the behavior of other drivers

Although proficiency in these skills is taught and tested as part of the driving exam, a 'good' driver can still be at a high risk of crashing because:

...the feeling of being confident in more and more challenging situations is experienced as evidence of driving ability, and that 'proven' ability reinforces the feelings of confidence. Confidence feeds itself and grows unchecked until something happens – a near-miss or an accident.^[3]

An AXA survey concluded Irish drivers are very safety-conscious relative to other European drivers. However, this does not translate to significantly lower crash rates in Ireland.^[4]

Accompanying changes to road designs have been wide-scale adoptions of rules of the road alongside law enforcement policies that included drunk-driving laws, setting of speed limits, and speed enforcement systems such as speed cameras. Some countries' driving tests have been expanded to test a new driver's behavior during emergencies, and their hazard perception.

There are demographic differences in crash rates. For example, although young people tend to have good reaction times, disproportionately more young male drivers feature in accidents,^[5] with researchers observing that many exhibit behaviors and attitudes to risk that can place them in more hazardous situations than other road users.^[3] This is reflected by actuaries when they set insurance rates for different age groups, partly based on their age, sex, and choice of vehicle. Older drivers with slower reactions might be expected to be involved in more accidents, but this has not been the case as they tend to drive less and, apparently, more cautiously.^[6] Attempts to impose traffic policies can be complicated by local circumstances and driver behaviour. In 1969 Leeming warned that there is a balance to be struck when "improving" the safety of a road:^[7]

Conversely, a location that does not look dangerous may have a high crash frequency. This is, in part, because if drivers perceive a location as hazardous, they take more care. Accidents may be more likely to happen when hazardous road or traffic conditions are not obvious at a glance, or where the conditions are too complicated for the limited human machine to perceive and react in the time and distance available. (This fact can be used to improve safety, by putting up signs in accident-prone locations, like ones stated above.)

This phenomenon has been observed in risk compensation research, where the predicted reductions in accident rates have not occurred after legislative or technical changes. One study observed that the introduction of improved brakes resulted in more aggressive driving,^[8] and another argued that compulsory seat belt laws have not been accompanied by a clearly attributed fall in overall fatalities.^[9]

In the 1990s Hans Monderman's studies of driver behavior led him to the realization that signs and regulations had an adverse effect on a driver's ability to interact safely with other road users. Monderman developed shared space principles, rooted in the principles of the woonerven of the 1970s. He found that the removal of highway clutter, while allowing drivers and other road users to mingle with equal priority, could help drivers recognize environmental clues. They relied on their cognitive skills alone, reducing traffic speeds radically and resulting in lower levels of road casualties and lower levels of congestion.^[10]

Some crashes are intended, staged crashes, for example, involve at least one party who hopes to crash a vehicle in order to submit lucrative claims to an insurance company. ^[11] In the 1990s, criminals recruited Latin immigrants to deliberately crash cars, usually by cutting in front of another car and slamming on the brakes. It was an illegal and risky job, and they were typically paid only $100. Jose Luis Lopez Perez, a staged crash driver, died after one such maneuver, leading to an investigation that uncovered the increasing frequency of this type of crash.^[12]

Motor Vehicle Speed[edit | edit source]

The U.S. Department of Transportation's Federal Highway Administration review research on traffic speed in 1998.^[13] The summary states:

• That the evidence shows that the risk of having a crash is increased both for vehicles traveling slower than the average speed, and for those traveling above the average speed.
• That the risk of being injured increases exponentially with speeds much faster than the median speed.
• That the severity of a crash depends on the vehicle speed change at impact.
• That there is limited evidence that suggests that lower speed limits result in lower speeds on a system wide basis.
• That most crashes related to speed involve speed too fast for the conditions.
• That more research is needed to determine the effectiveness of traffic calming.

The Road and Traffic Authority (RTA) of the Australian state of New South Wales (NSW) asserts speeding (traveling too fast for the prevailing conditions or above the posted speed limit^[14]) is a factor in about 40 percent of road deaths.^[15] The RTA also say speeding increases the risk of a crash and its severity.^[15] On another webpage, the RTA qualify their claims by referring to one specific piece of research from 1997, and stating "research has shown that the risk of a crash causing death or injury increases rapidly, even with small increases above an appropriately set speed limit."^[16]

The contributory factor report in the official British road casualty statistics show for 2006, that "exceeding speed limit" was a contributory factor in 5% of all casualty crashes (14% of all fatal crashes), and that "traveling too fast for conditions" was a contributory factor in 11% of all casualty crashes (18% of all fatal crashes).^[17]

Driver Impairment[edit | edit source]

Driver impairment describes factors that prevent the driver from driving at their normal level of skill. Common impairments include:

Alcohol

In Canada 33.8% of motor vehicle deaths were associated with alcohol use.^[18][19] See also: alcohol-related traffic crashes in the United States

Physical Impairment

Poor eyesight and/or physical impairment, with many jurisdictions setting simple sight tests and/or requiring appropriate vehicle modifications before being allowed to drive

Youth

Insurance statistics demonstrate a notably higher incidence of accidents and fatalities among teenage and early twenty-aged drivers, with insurance rates reflecting this data. Teens and early twenty-aged drivers have the highest incidence of both accidents and fatalities among all driving age groups. This was observed to be true well before the advent of mobile phones. Females in this age group suffer a somewhat lower accident and fatality rate than males but still well above the median across all age groups. Also within this group, the highest accident incidence rate occurs within the first year of licensed driving. For this reason many US states have enacted a zero-tolerance policy wherein receiving a moving violation within the first six months to one year of obtaining a license results in automatic license suspension. No US state allows fourteen year-olds to obtain drivers licenses any longer.

Old Age

Old age, with some jurisdictions requiring driver retesting for reaction speed and eyesight after a certain age

Sleep Deprivation

Fatigue

Drug Use

Including some prescription drugs, over the counter drugs (notably antihistamines, opioids and muscarinic antagonists), and illegal drugs.

Distraction

Research suggests that the driver's attention is affected by distracting sounds such as conversations and operating a mobile phone while driving. Many jurisdictions now restrict or outlaw the use of some types of phone within the car. Recent research conducted by British scientists suggests that music can also have an effect; classical music is considered to be calming, yet too much could relax the driver to a condition of distraction. On the other hand, hard rock may encourage the driver to step on the acceleration pedal, thus creating a potentially dangerous situation on the road.^[20]

Combinations of Factors

Several conditions can work together to create a much worse situation, for example:

• Combining low doses of alcohol and cannabis has a more severe effect on driving performance than either cannabis or alcohol in isolation.^[21]
• Taking recommended doses of several drugs together, which individually do not cause impairment, may combine to bring on drowsiness or other impairment. This could be more pronounced in an elderly person whose renal function is less efficient than a younger person's.^[22]

Thus there are situations when a person may be impaired, but still legally allowed to drive, and becomes a potential hazard to themselves and other road users. Pedestrians or cyclists are affected in the same way and can similarly jeopardize themselves or others when on the road.

Road Design[edit | edit source]

A 1985 US study showed that about 34% of serious crashes had contributing factors related to the roadway or its environment. Most of these crashes also involved a human factor.^[1] The road or environmental factor was either noted as making a significant contribution to the circumstances of the crash, or did not allow room to recover. In these circumstances it is frequently the driver who is blamed rather than the road; those reporting the accident have a tendency to overlook the human factors involved, such as the subtleties of design and maintenance that a driver could fail to observe or inadequately compensate for.^[23]

Research has shown that careful design and maintenance, with well-designed intersections, road surfaces, visibility and traffic control devices, can result in significant improvements in accident rates. Individual roads also have widely differing performance in the event of an impact. In Europe there are now EuroRAP tests that indicate how "self-explaining" and forgiving a particular road and its roadside would be in the event of a major incident.

In the UK, research has shown that investment in a safe road infrastructure program could yield a ⅓ reduction in road deaths, saving as much as £6 billion per year.^[24] A consortium of 13 major road safety stakeholders have formed the Campaign for Safe Road Design, which is calling on the UK Government to make safe road design a national transport priority.

References[edit | edit source]

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