Looking at average population density is nonsensical - people aren't uniformly distributed. Most live in relatively dense urban areas and most trips they make a

Looking at average population density is nonsensical - people aren't uniformly distributed. Most live in relatively dense urban areas and most trips they make are local. America isn't special in any of these regards. The advantages of road networks as efficient means of point-to-point transportation disappear very quickly as the rate of non-point-to-point trips increases. Static routes like commuting and grocery shopping account for most traffic and are incredibly wasteful. You aren't stuck in traffic because of bespoke trips that necessitate a car, you're stuck because people make the exact same trip from A to B and back every single day.