Driving usually changes in small steps. A new scrape on the bumper, a mirror pushed in a different direction, a route that has quietly shrunk to two streets. Nobody sits the parent down to announce it. You notice the car before you notice the change, which is why the car is a good place to start looking.
Local option: New Plan Care gives families in the St. Louis area in-home help so a parent can stay home: companionship, help with bathing and dressing, meals, and overnight care. Call (314) 405-0887.
Check the car itself
Walk around the vehicle once a week and note any new dents, scrapes, or mirror damage. Look at the tires, the headlights, and any warning light on the dashboard. Check whether the car is parked in the same place it always was, or whether it has been moved and parked badly. A car that sits unused for long stretches, or has new damage nobody can explain, is worth a conversation.
Ride along and watch
Make a short trip with your parent on a route you both know. Pay attention to how they check the mirrors, how they handle turns and lane changes, whether they hesitate at intersections, and whether they seem unsure about the road. Note whether they ask for directions on a route they used to take without thinking. Write down what you saw as specific observations, not verdicts.
Notice the habits around the drive
Parents often adapt before they admit a change. Watch for driving only in daylight, only on the same few roads, only when the weather is clear, or asking a family member to drive on any trip that feels long. Those adjustments are useful information. They tell you the parent is aware of a limit even if they have not said so.
Write down specific incidents
When something happens, record what it was, where it happened, the time of day, and whether anyone was hurt or any property was damaged. A written list is more useful than a general worry, and it is what a doctor or the licensing office will ask about if you raise the question.
Ask the right people the right questions
Ask the parent's doctor whether a driving evaluation is appropriate and what the process involves. Check the state licensing agency's public rules for older drivers, and ask the auto insurer what the policy requires and whether any notice must be given. Those are questions to ask, not legal advice, and the answers depend on your state and your parent's situation.
Before any conversation about keys, make a plan for how your parent will get to appointments, groceries and friends if driving stops. A transportation plan written down in advance makes the hard conversation easier for everyone. The Sources page lists the public materials this desk uses, if you want to read further.