Older Drivers

Type of Problem Being Addressed

General Description of the Problem

The United States is aging-its older population will double over the next 30 years (Exhibit III-1). By 2030, one in five Americans will be 65 or older. As people age, a decline in sensory, cognitive, or physical function can make them less safe drivers, as well as more vulnerable to injury once in a crash. Yet older Americans depend on automobiles to meet their transportation needs. According to national transportation survey data, 90 percent of trips taken by older adults are by personal vehicle. Of that 90 percent, 70 percent involve the older adult driving the vehicle.

Exhibit III-1
Projected Growth in U.S. Population Age 65+
(Source: Administration on Aging, “A Profile of Older Americans,” 2000,
www.aoa.gov/prof/statistics/profile/2002/2.asp)

How safe are older drivers? The answer depends upon how “safety” is measured. On a licensed driver basis, older adults are among the safest on the road (Exhibit III-2). The average annual number of crashes in the United States is 68 per 1,000 licensed drivers, while the corresponding rate for drivers aged 65 and older is only 37. The picture changes somewhat when crash rates are calculated on the basis of miles traveled. Using this measure of exposure, older adults are at increased crash risk (Exhibit III-3). The increase in risk is evident for 65-74 year olds, but becomes even more pronounced with increased age. Drivers age 85 and older have about the same high crash rate per mile driven as 20-24 year olds.

The real safety concern for older drivers arises when one takes into consideration their increased likelihood of being injured or killed in a crash. Compared with an overall fatality rate of 2 per 1,000 crashes, persons ages 65-74 have a fatality rate of 3.2. For those 75-84, the rate is 5.3, and at 85 and above it climbs to 8.6. If instead of measuring safety in terms of crashes per licensed driver and crashes per mile traveled, one measures it in terms of fatalities per licensed driver and fatalities per mile traveled, there is clearly cause for concern (Exhibits III-4 and III-5). Both begin to increase by age 55, and the increase is especially dramatic for persons age 85 and older.

EXHIBIT III-2
Annual Crashes per 1,000 Licensed Vehicle Drivers by Age of Driver
(Source: Cerrelli, 1998)

EXHIBIT III-3
Crashes per Million Miles Traveled by Age of Driver
(Source: Cerrelli, 1998)

EXHIBIT III-4
Fatalities per 1,000 Licensed Drivers by Age of Driver
(Source: Cerrelli, 1998)

EXHIBIT III-5
Fatalities per 100 Million Vehicle Miles Traveled by Age of Driver
(Source: Cerrelli, 1998)

The real safety concern for the older driver arises when one takes into consideration their increased likelihood of being injured or killed once in a crash. Compared to an overall fatality rate of 2.0 per 1,000 crashes, persons ages 65–74 have a fatality rate of 3.2. For those ages 75-84, the rate is 5.3, and for those ages 85 and above it climbs to 8.6. If instead of measuring safety in terms of crashes per licensed driver and crashes per mile traveled, we measure it in terms of fatalities per licensed driver and fatalities per mile traveled, there is clearly cause for concern (Exhibit III-4 and Exhibit III-5). Both begin to increase by age 55, and the increase is especially dramatic for persons age 85 and older.

Taken together, the data suggest that the safety problem confronting older adults is as much an issue of crash survivability as it is crash avoidance. This safety problem is not likely to improve in the future without the highway safety community’s broad and concerted efforts.

Specific Attributes of the Problem

Studies have shown that compared with younger drivers, older drivers are more likely to be involved in crashes at intersections, especially when attempting a left-turn maneuver. Drivers 85 and older are more than 10 times as likely as 40-49 year olds to be in fatal multiple-vehicle crashes at intersections. Based on analysis of North Carolina crash data, older drivers are also over-represented in crashes involving right turns, U-turns, backing, starting in the roadway, and parking or leaving a parked position (Reinfurt et al., 2000). The fact that older drivers’ crashes are more likely to involve angle collisions and side impacts than other age groups are likely contributors to older drivers’ higher injury rates, despite the generally low speeds involved (Exhibit III-6).

EXHIBIT III-6
Of People who Died in Collisions, Percentage who Died in Angle Collisions
(Source: NHTSA, 1997)


About 55 percent of people age 85 and older who died in collisions died in angle collisions. This percentage is significantly lower for younger people. Only about 25 percent of people age 16-19 who died in collisions died in angle collisions.

While much attention has been given to older drivers’ higher frequency of intersection crashes, less attention has been given to their considerably lower frequency of single vehicle, run-off-roadway (ROR) crashes. Driving exposure may play an important role in both situations, since older drivers are more likely to crash at intersections and a greater proportion of their driving takes place in cities and on local streets. At the same time, older drivers may be less likely to run off the roadway, as they drive less on rural, two-lane roadways where these types of crashes typically occur.

The likelihood of being at fault in a crash has also been shown to increase with age: nearly 70 percent of drivers 75 and older involved in fatal two-vehicle crashes were at fault, compared with less than 40 percent for drivers 45-64 (Exhibit III-7). Specific crash types where older drivers are increasingly likely to be found at fault include angle collisions (usually involving two vehicles passing through an intersection on perpendicular paths), left and right turns across traffic collisions, and slowing or stopping collisions (Stewart et al., 1999). The fact that all of these collision types typically occur at intersections suggests that intersections pose problems for older drivers and that these problems do not stem merely from older drivers’ being more exposed to intersection situations.

As noted above, declining functional abilities may be responsible for older drivers’ increased risk of crashing. As people age, there is a decline in many of the abilities considered necessary to safely operate a motor vehicle. Older people, as a group, have reduced visual acuity, narrower visual fields, poorer nighttime vision, greater sensitivity to glare, slower reaction times, more attention deficits, reduced muscle strength, reduced flexibility and range of motion, and other declines in visual, cognitive, and psychomotor function that can adversely affect driving. Older people are also more likely to suffer from chronic medical conditions and to rely on medications, both of which can result in temporary or long-term functional losses. Exhibit III-8 identifies some of the key driving-related functional abilities that have been shown to decline with age.

EXHIBIT III-7
Percent of Time Drivers Are at Fault when They Are Involved in a Two-Vehicle Crash (by Driver Age)
(Source: Stewart et al., 1999)

EXHIBIT III-8
Key Functional Abilities Affected by Aging and Their Relationship to Driving
(Adapted from Staplin et al., 1999)

Functional Domain

Specific Area of Functional Loss

How the Function Relates to Driving

Vision

Reduced visual acuity

Visual acuity is used to resolve fine detail; it is used to see roadway targets that have high brightness or color contrast with the surrounding background area and that have sharply defined edges, such as letters on road signs.
Reduced visual contrast sensitivity Contrast sensitivity allows an individual to see targets that do not differ greatly in brightness or color from the surrounding background area or that may have “fuzzy” or ill-defined edges. Examples are when the edge of the road has a worn/faded or missing edgestrip or the color of the shoulder is similar to that of the paved surface.
Increased susceptibility to glare/slower glare recovery An older person’s vision suffers more than that of a younger person when glare enters the eye (because of, e.g., vitreous changes in the eye associated with aging and pathology such as cataracts). The stray light masks or interferes with focal vision and lengthens the time, after exposure to the disabling effects of glare, before roadway targets can be seen as well as before the glare was introduced. At night, headlights viewed in oncoming traffic or headlights viewed in rearview mirrors produce this effect, and during the day, sun glare can cause similar problems.
Reduced sensitivity to changes in angular size and motion Motion detection influences judgments about an object’s distance and how fast it is moving, for example, a car approaching as a driver waits to turn left at an intersection. Correct judgments of gaps in traffic for turning and merging depend strongly upon how quickly and accurately the brain can interpret changes in the size of the image that is formed on the retina at the back of the eye when his/her gaze is focused on a distant object.
Poorer visual pattern perception and visualization of missing information Drivers need this perceptual skill to extrapolate from only partial information, provided by a few visual elements, and to “construct” a whole image of a scene. This skill permits a driver to recognize a potential hazard when only part of it is in direct view, such as a pedestrian or another vehicle about to enter one’s path from behind some obstruction.
Less efficient visual search Visual search abilities contribute to how fast a person can find and identify safety threats and other critical information on an ongoing basis while driving, as when a driver scans the always-changing roadway scene ahead to look for a sign, landmark, or other directional information.
Reduced area of visual attention Visual attention relates to a portion of the visual field where a person not only is capable of seeing an object, but also can process information about it and respond quickly enough to avoid a crash if it is a traffic hazard. The risk of colliding with vehicles, pedestrians, and cyclists entering from the side of the road or at an intersection increases significantly as this area of visual attention, sometimes referred to as the “useful” or “functional” field of view, shrinks.
Cognition Impaired selective attention ability A person must use selective attention continuously while driving to filter out less important events and information and to “hone in” on just those few things that are most safety critical. Though not conscious of it, drivers must constantly filter out millions of times as much sensory information as they actually use to make decisions and control their vehicles. Thus, intact selective attention abilities are essential to anticipate and respond appropriately to hazards.
Less efficient divided attention and slower attention switching Attentional abilities come into play when a driver must monitor and respond effectively to multiple sources of information at the same time. For example, a driver entering a freeway must track the curvature of the ramp and steer appropriately, keep a safe distance behind the car ahead, and check for gaps in traffic on the highway, while simultaneously accelerating just enough to permit a smooth entry into the traffic stream. Distractions inside and outside the vehicle may compound the problem.
Less efficient working memory processes This relates to the frequent need to think about and recall recently learned information while driving, without any lapses in safely controlling one’s vehicle-for example, being able to remember and apply a simple set of navigational instructions memorized before a journey while driving in heavy traffic. A decline in this functional ability may occur gradually through normal aging processes and become sharply accelerated with the onset and progression of dementia.
Psychomotor and Physical Function Loss of limb strength, flexibility, sensitivity, and/or range of motion Declining functionality in the limbs affects the ability to quickly shift the right foot from accelerator to brake when the situation demands, to apply correct pressure for appropriate speed control, and to safely maneuver the car through turns and around obstacles.
Reduced ability to rotate the head and neck Driving commonly requires that a driver be able to (re)direct his/her gaze in many different directions to check for potential conflicts; most obvious are the familiar “left-right-left” check before crossing an intersection and looking over one’s shoulder before merging with traffic or changing lanes.