&gt; In practice, people can tell the design speed of a road<p>I think there have been quite a few studies showing most people think they are above average at driving. I don&#x27;t think people do this at all. I think they are overconfident, hurrying apes, with no real conception of stopping distance or kinetic energy, aiming to just miss each other with these multi-ton projectiles. It&#x27;s sadly not  surprising how many people are killed on the roads.