I see that argument a lot but am not really convinced by it. Sure the US has a bunch of land for the population it has, but that is mostly because it has a lot

I see that argument a lot but am not really convinced by it. Sure the US has a bunch of land for the population it has, but that is mostly because it has a lot of unpopulated areas in the middle. There's no reason that the actual urban areas need to be less dense and that's where most of the trips happen. There's plenty of countryside outside London or Paris to expand into, so European cities aren't denser because space is at a premium. I think the real difference is that even in urban areas the US has a much larger tendency to build suburban, single-family housing whereas in Europe apartment buildings are much more common. People prioritize living close to the city center and having a 5 minute commute over having a house and a garden and spending 1+ hours on the highway every day. So it's much more about local density and that is a function of urban planning decisions/preferences and has nothing to do with TotalPopulation/TotalLandMass.