We don't have to guess. Netherlands has 500 people per km2. USA has 36. Road that connects 3 biggest cities in Netherlands has 3 lanes in each direction: https

We don't have to guess. Netherlands has 500 people per km2. USA has 36. Road that connects 3 biggest cities in Netherlands has 3 lanes in each direction: https://www.google.com/maps/@52.1822053,4.5947627,3a,75y,47.43h,68.18t/data=!3m6!1e1!3m4!1sjWbzg1ULl7plGJgQdewN-A!2e0!7i16384!8i8192?entry=ttu https://www.google.com/maps/@52.1822053,4.5947627,3a,75y,47.... Your average road in Netherlands looks like this: https://www.google.com/maps/@52.1968565,4.592548,3a,75y,58.84h,70.23t/data=!3m7!1e1!3m5!1sJErVQHv6sBE0By1yjRNClw!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fpanoid%3DJErVQHv6sBE0By1yjRNClw%26cb_client%3Dmaps_sv.tactile.gps%26w%3D203%26h%3D100%26yaw%3D170.54272%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192?entry=ttu https://www.google.com/maps/@52.1968565,4.592548,3a,75y,58.8... You cannot directly translate between countries with such difference in population density obviously, but if anything - the more people USA has - the bigger gains are there to be realized by switching to more efficient mode of transport.