The following factors should not rule out driving, but they can elevate risk and warrant monitoring:

• Health conditions. Physical and mental impairments that accompany aging, from Parkinson's disease to dementia, can compromise driving agility and judgment. If you have questions about someone's ability to drive given his health problems, consult with his physicians, if possible, and raise the issue of driving safety. (Keep in mind that his physician can't talk to you without his permission, unless you have power of attorney.)
• Vision impairment. Vision is obviously a key component of driving ability. In fact, according to Elizabeth Dugan, author of The Driving Dilemma, "90 percent of the information needed to drive safely relates to the ability to see clearly." From accurately reading the speedometer to detecting pedestrians on the side of the road, good driving requires good eyesight. But deterioration in vision is an inevitable effect of aging; in people 75 and older, vision impairment rates increase significantly, according to the Centers for Disease Control. As the eye ages, far less light reaches the retina, for one thing. Older eyes are also more susceptible to cataracts, glaucoma, and other problems that impair vision. Encourage your family member to have regular eye exams, and check in with his eye doctor if you have concerns.

• Hearing impairment. Few people age without some deterioration in their hearing. In fact, one-third of those over 65 have hearing problems. Hearing loss can happen gradually, without realizing it, and undermine his ability to hear horns, screeching tires, sirens, and other sounds that would normally put someone on high alert. Make sure the person in your care has regular hearing tests.

• Prescription drug use and drug interactions. Many drugs can compromise driving ability by causing drowsiness, blurred vision, confusion, tremors, or other side effects. Certain drugs taken in combination can also interact and cause serious problems. If your family member takes a lot of pills each day, as many elderly people do, educate yourself about the drugs and possible side effects. Even herbal remedies and over-the-counter medications can affect driving ability. Talk to your family member's physicians and pharmacist, and be sure to ask about possible drug interactions.

• Alcohol abuse. Drinking and driving is always a dangerous combination; add old age to the mix and you have a disaster waiting to happen. As people age, alcohol remains in the system longer and tolerance declines. Also, elderly folks are likely to be on medication, which can exacerbate the effects of alcohol. Given these risks, and the difficulty of gauging exactly how much alcohol will impair an individual's driving, Elizabeth Dugan's advice is simple: "If you drink, don't drive. Period." If you suspect that your family member is drinking and driving, don't wait to take action.