For instance, a decline in peripheral vision may impact the ability to pass approaching vehicles safely, and the decreased range of motion in an older person's neck may impair the ability to look behind when backing up. Also, reaction time decreases by almost 40% on average from age 35 to 65 (Jackson, 1999).
It also appears that the aging process may affect cognitive skills. Short-term memory loss, for instance, can decrease driving skills by interfering with an individual's ability to process information effectively when merging onto a highway into traffic or changing lanes. Such issues are magnified when driving under stressful situations. The higher incidence of cognitive impairment, particularly dementia, among older men and women leads to an increased risk of accident involvement (Jackson, 1999).
According to AARP, as a group, persons age 65 and older are relatively safe drivers. Although they represent 14% of all licensed drivers, they are involved in just 8% of police-reported crashes and 11% of fatal crashes. In comparison, drivers age 16 to 24 are involved in 26% of police-reported crashes and 26% of fatal crashes, but represent only 14% of licensed drivers. Individuals over 65 also drive fewer miles on average than any other age group.
However, when they crash, the situations and reasons are normally different from younger drivers. Older drivers' crashes occur most often when are turning left, whereas younger drivers crashes usually take place while they are driving straight ahead. Older drivers fail to yield right of way or not respond properly to stop signs and traffic lights. Younger drivers speed follow too close. Among all drivers age 65 and older, it is the oldest ones who pose more risk to themselves and to public safety. For all adults age 25 to 64, and for adults age 65 to 69, the rate of crashes per miles driven is relatively constant. The rate begins to rise at age 70, and increases rapidly at age 80.
In addition, the aging may not be aware of their decreasing driving ability. Seniors who are experiencing cognitive or physical decline shouldn't be the ones to judge their own driving abilities. Bonnie Dobbs, an assistant professor at the University of Alberta in Canada, found that 98% of elderly drivers with impairments severe enough to hinder driving ability think they are average or above-average on the road (Corcoran, 2003, 16).
A common consequences of aging is a decline in motoric function and the ability to learn new motor skills. These declines in motoric function and motor learning are associated with increased risks of falling and mortality in older individuals. Also, musculoskeletal impairments often can impact driving safety in the elderly. Conditions such as rotator cuff tendinitis may make turning a steering wheel more difficult. Under emergency conditions, the older adult driver may have trouble avoiding an accident or reducing its severity by avoiding a direct impact. Recently, a study suggested that elderly drivers are more likely to be involved in accidents that involve angles or turning. Arthritis in the neck or shoulders may result in a limited ability to turn the head, reducing the ability to scan efficiently for traffic at an intersection. Finally, reflexes often begin to diminish in the elderly, which puts them at greater risk for a traffic accident.
It is well recognized that the occurrence of impaired vision and hearing increases with age. Driving is a complex task that depends on sensory acuity, ability to process a large number of environmental stimuli simultaneously, cognitive capacity to recognize correct inferences from incoming data and to formulate a correct response, and motor ability to operate the vehicle's controls (McCloskey, 1999, 267). Although impairments in any of these faculties may higher the risk of crash, some investigators propose that the presence of sensory impairments is particularly important. Common visual deterioration occurs through cataracts, glaucoma, age-related macular degeneration, diabetic retinopathy, optic atrophy, corneal dystrophy, and effects of stroke.
As humans age, the ability to see details at a distance declines and they have a harder time focusing on nearby objects. This presbyopia is an age-related process that results from the loss of flexibility in the eye's lens and is different from near- and farsightedness. As it progresses, presbyopia can pose safety problems for drivers such as greater difficulty reading dashboard control panels and instrumentation (Industrial Engineer, 2004). Aging is associated with a progressive deficit in the resolution of fine visual details. Acuity for high-contrast targets, approximately 20/18 at age 20, falls to about 20/30 by age 70. In addition, failure to meet a 20/40 acuity cutoff under nighttime testing occurs with disproportionate frequency among older drivers.
The reduction in the size of an elder's visual field has been implicated as a major cause of automobile accidents involving drivers of advanced age. Drivers with peripheral visual deficits have collision rates twice as high as those with normal peripheral vision. (Beer, 2000, 233). Neuron loss to the peripheral retina can also lead to limited visual acuity in the periphery. This is why driving at twilight may present the most difficulty: The peripheral retina is extremely sensitive to decreased light. Another study out of the Department of Ophthalmology and Visual Sciences of the University of Illinois, Chicago Eye Center noted evidence of compensation for visual impairment in an age-related macular degeneration group, as compared to similar-age subjects with normal vision, in four major areas: (1) not driving in unfamiliar areas, (2) traveling at low speeds, (3) self-restricting nighttime driving, and (4) taking fewer risks while driving (e.g., not changing lanes) (Szlyk, 1995, 1033). Millions of elderly people experience vision loss as a result of age-related macular degeneration. Although these people rarely become blind, they do experience difficulty performing daily activities that require central vision such as reading or driving a motor vehicle
Numerous older adults suffer visual impairment due to cataracts more often than any other single cause. More than half of adults older than age 65 have cataracts, which is slightly more frequent in African-Americans. Retrospective reviews have shown that among older drivers, presence of cataracts was associated with an increased frequency of a recent motor vehicle accident (MVA) when compared with persons free of this eye condition. The per capita MVA rate in older licensed drivers (40/1000) is substantially less than in persons younger than 25 (140/1000), but this is largely a result of the many fewer miles driven by older persons than younger. Hence, the per-mile driven rate of MVA among older drivers is actually comparable to that of the highest risk younger drivers (Kuritzky, 2002, 23).
In 2001, the states of Alabama and Kentucky tested about 300 drivers with an eye examination that went beyond the standard eye chart to assess "useful field of view," which included visual processing, the ability to filter out visual distractions, and other factors. Three years later, the drivers whose test results showed they had an impaired useful field of view were more than twice as likely to have been in an accident than those who showed no impairment. Standard eye tests did not predict accident risk (Harvard Health Letter, 2002, NA).
A significant percentage of the elderly suffer hearing loss. This presbycusis is characterized by a decline in the ability to hear sounds at certain frequencies and at low decibel levels. To determine how diminished hearing might increase the risk of motor vehicle collision injuries in older drivers, McCloskey et. al conducted a population-based case-control study at a large Health Maintenance Organization (HMO). All study subjects were HMO members who were licensed drivers age 65 or over. They found that owners of hearing aids and those who used a hearing aid while driving were at increased risk of having an injury collision.
A number of other medical illnesses may possibly hinder the elderly driver. One of the most serious areas of concern with aging is dementia or, in the extreme, Alzheimer's disease. Individuals with Alzheimer's disease or a related disorder become steadily more impaired in their ability to handle such functions as driving. They can exhibit symptoms such as memory loss, disorientation, and alterations in visual and spatial perception that often lead to their getting lost, forgetting driving rules or having slowed-down reaction times. Although an individual with early dementia may not appear to have such problems, the disease may eventually affect his or her motor coordination, judgment and concentration. In addition, at all steps of hindrance driving ability is likely to worsen during times of high stress.
Normally, it is not unusual for individuals with dementia and their families to have different opinions on the older persons' driving ability. However, while respecting that person's desire to drive, family members must put safety first. Because they do not want to lose their independence, some people with dementia may insist on continuing to drive even when their licenses are revoked. Unfortunately, as a last resort, caregivers and family members may need to prevent access to the vehicle.