Thoughts
With practice, I wouldn’t downplay a human’s ability to judge speed. Baseball players can time a swing to a fraction of a second, with a
ball moving faster than a car. It’s a little harder to judge acceleration, but most drivers have had practice.
Where I think there’s a lot of uncertainty on the human driver’s part is knowing the size and position of their own car.
(Originally written as an HN comment, but I don’t think it actually adds anything to the conversation.)