"dangerously" and "fast" are not synonyms (while drunkess obviously is dangerous regardless). The 280 in San Mateo County is designed for 80MPH, with banked turns, gentle curves, etc. The speed limit is of course 65. If most people are driving 80-85, and you enter that highway and drive 60, which is a perfectly reasonable speed according to the speed limit, you are much more likely to cause an accident than if you just drive the speed of the people around you.

It's fine to point out that many people are terrible drivers and that a given crash that happens is more dangerous at a higher speed and if everybody were to drive under 60 at all times we'd all be safer, but clearly that will never happen unless we install a totalitarian government, put governors on all cars and give prison time for disabling them, with enforcers stationed everywhere to monitor. But no democracy would vote for that, so I don't think it's worth spending much mental energy on such hypotheticals.

> encourage

I think just the opposite: My feature would encourage people like me, who drive a "fast car" and can occasionally accidentally go too fast if a road is especially uncongested, to slow down to the speed that is customary or that others are driving, by reminding me that I could get a ticket and that driving faster than everyone else is dangerous.