The Reasons for Problems

Driving involves the precise execution of simultaneous tasks (such as braking and steering). These tasks variously require several attributes, including the following:

• A clear mind
• Attention and mental focus
• Swift reaction time
• Coordination
• Adequate strength
• Good range of motion of the upper body (upper trunk, shoulders, and neck)
• Good vision and hearing
• Good judgment

Deficits in any of these attributes can greatly affect driving performance. Such deficits can result from several causes.

Virtually all of these attributes yield to some degree to the passage of time: Aging itself usually results in a gradual and subtle decline in a person's strength, coordination, reaction time, and ability to concentrate. Vision (especially at night) and hearing also decrease with aging.

Medical disorders that are more common among older people can prove especially troublesome for older drivers. For example, the blood sugar level of drivers with diabetes may rise too high or drop too low. Such changes can interfere with thinking clearly, attention and mental focus, and vision.

Older drivers with dementia (including Alzheimer's disease) can have poor judgment and concentration, a dangerous prospect when driving. Even when dementia is in its early stages, a driver may become more easily lost or more easily confused in congested traffic.

Strokes or so-called ministrokes (transient ischemic attacks, or TIAs) can slow reaction time and reduce coordination. Seizures can abruptly cause people to become unaware of their surroundings or even lose consciousness. A recent heart attack may increase a driver's risk of fainting or experiencing light-headedness.

Arthritis causes joint pain and stiffness, limiting a person's range of motion and possibly interfering with the ability to operate a car's controls. For example, pain and stiffness in the knees or hips may affect a person's ability to press the brake pedal. Arthritis can make turning the head (as is necessary when turning or reversing a car) painful and difficult.

Glaucoma and macular degeneration are eye disorders that lead to problems when driving at twilight or at night. Glaucoma can also narrow the field of vision so that cars and other objects alongside the driver are difficult to see. Cataracts, which occur almost exclusively among older people, can cause glare from oncoming headlights or street lamps.

Many older people take drugs that can have undesirable side effects. Side effects can include sleepiness, dizziness, confusion, and other symptoms that interfere with driving. Nonprescription antihistamines and sleep aids are among the drugs that produce these side effects.

For some older people, the only "deficit" in driving ability is simply a lack of driving experience. This deficit is often the case when an older person (usually a woman) learns to drive only after a spouse dies.