My mom is 83, has very poor vision, has suffered a stroke, but continues to drive. Because we expressed concern about her abilities, her license was suspended for 6 months after the stroke. She had to go to driving rehab, where she got a very thorough neurological exam, had to pass the written test, pass the road test, and write a sentence to demonstrate that she could express a complete thought. She was told to drive only during daylight hours, no interstate driving, drive only to familiar places, and to complete a driving class for senior citizens. As time passes, she finds more and more "familiar" places, she sometimes gets home after dark during the fall and winter, and she has refused to take the senior driving course. She has been involved in one accident that was the other driver's fault. She has been such a bad driver for so many years that nobody will ride with her, not since the late 80's. Noboby has taken her keys yet, but I have sent in a form to DMV. She will probably disown me if the state actually investigates my concerns.
There are an awful lot of people on the road who should not be driving. When I look for my former students at the Clerk of Courts site, I see that most of them have recurring charges for driving with no license. My guess is that they could not read well enough to pass the written exam. Some of them had zero impulse control, which is a recipe for disaster. When I look at the records of my husband's nephew or a particular neighbor, I see DUIs, driving with license suspended or revoked, speeding, all listed as first offenses even though there are multiple charges for each type of offense.
If you could remove from the road every driver who does not have a valid license, traffic would probably decrease considerably. We wouldn't be any safer on the road, though, because there are all those idiots who think they are good drivers because they have never had a wreck. They should give all that credit to those of us who are quick enough to move out of their way!