I can't actually find anything suggesting that the most dangerous roads are not highways. I really tried. Perhaps there are more small accidents on local roads, but they would tend to be less dangerous. The evidence suggests that highways are significantly more fatal[0].

Also, Autopilot is not essential forced off for anything but highways. That is just factually incorrect. Notably, straight-aways are where Autopilot works best and are the most dangerous by crashes.[1]

I found data suggesting that a lot of accidents happen because people rear-end stopped cars at intersections[2] and issues with navigating intersections[3]. That is an area where Autopilot is pretty great today.

0: https://www-fars.nhtsa.dot.gov/People/PeopleAllVictims.aspx (see last table)

1: https://www-fars.nhtsa.dot.gov/Vehicles/VehiclesAllVehicles.... (see last table)

2: https://www.hg.org/legal-articles/when-and-where-do-car-acci...

3: https://www-fars.nhtsa.dot.gov/Vehicles/VehiclesLocation.asp...