Help for knowing when it's time to take the keys away from a loved one with dementia

(ARA) - The decision on when an aging loved one should stop driving is never an easy one, but the issue becomes even more complex - and heart-wrenching - when the loved one also suffers from dementia or Alzheimer's disease. How do you know when someone is no longer safe to drive? How do you gently explain this to him? How do you take away her car keys without taking her dignity as well?