What you say is wrong because much of the traffic on the subway and busses are commuters who travel from the suburbs. In Manhattan where I live, commuters near

What you say is wrong because much of the traffic on the subway and busses are commuters who travel from the suburbs. In Manhattan where I live, commuters nearly double the daytime population from 1.6 million to 3.1 million. http://cityroom.blogs.nytimes.com/2013/06/03/commuters-nearly-double-manhattans-daytime-population-census-says/ http://cityroom.blogs.nytimes.com/2013/06/03/commuters-nearl... increasing the building density would simply enable those people who are less fortunate than many of us on HN to also live in Paris. Moreover, I can't speak for Paris but for certain I know in NYC/Manhattan the subways are not running nearly at their capacity. IIRC, the capacity could double if they automated the systems (which they are taking a very long time to do). The same may be true of Paris.