It isn't always immediately obvious when an elderly person begins to have trouble driving. Your parent may not notice that her driving skills are deteriorating or may not want to acknowledge it -- and you may not care to either. Of course you want your parent to maintain her independence as long as possible, but don't wait for an accident to happen before you intervene. Here's what you can do:

Take several drives with your parent at the wheel, and observe her driving with an open mind.

Is she tense? Does she lean forward in her seat and appear worried or preoccupied? Does she often express irritation at other drivers? Does she seem particularly tired after driving? If so, she's probably beginning to have some anxiety about driving.

Notice whether your parent is reluctant to drive.

She may, for example, decline invitations to social events that require her to drive, particularly at night. This may be her way of acknowledging that she's aware of her own limitations and is taking steps to avoid an accident.

Watch for slowed reaction time.

Does she consistently wait too long to respond to traffic lights or other driving cues?

Notice her awareness of her driving environment.

Does she tailgate, for example? Does she stay in her own lane or let the car drift very close to the centerline? Does she complain of getting lost more than she used to?