In Manhattan it's 23% (http://www.nycedc.com/blog-entry/new-yorkers-and-cars). This is quite scarce relative to the rest of the USA and indeed even relative to the suburban boroughs of the greater New York City metro area. For the US the last average I saw (World Bank data http://web.archive.org/web/20140209114811/http://data.worldb...) was 81%.