There's still plenty of cars in europe. Biggest advantage of europe is even the major cities are only so large in footprint, like even berlin is barely over a dozen miles across. Major US cities could be 40-60 miles across. Greater LA maybe over 100 miles across depending on how you measure, all contiguous development. The northeast corridor is nearly contiguous urban/suburban development over a ~450 mile snake from washington dc to boston. Makes a little 10 mile rail line in berlin capture a much greater share of potential trips within the berlin urban area than a 10 mile rail line pretty much anywhere in the US. LA has a light rail line that is over 50 miles long.