(1) Sure there are a few places in America that approach Europe-levels of density, but those are clear exceptions. If we're going to speak in generalities, the general rule is that America is far less dense than Europe. (2) Is public transportation in the Washington D.C. to New York corridor, or within Boston, really worse than most European urban areas? It doesn't seem it's much worse. "Though transit usage in New York compares favorably with that in many large Western European cities, few other large American cities have ridership levels even half that of greater New York. Only five other urban areas—metropolitan Boston, Chicago, San Francisco, Philadelphia, and Washington (D.C.)—have annual transit ridership levels exceeding 75 trips per capita." --https://nap.nationalacademies.org/read/10110/chapter/4#28