There's also enormous variety which may change with the season, weather, washouts, and how recently the road has been repaired across large stretches of the US West, among other areas. Even with a map, the difference between well-graded dirt road and competent high clearance 4WD vehicle and driver needed is often far from obvious.

Furthermore, some visitors not familiar with such areas tend to assume that, if a road is on the map, that means it's fine to take in their passenger car.