[jrobbins]

I see it as basically Malthusian: people will keep driving until it is so unpleasant that they don't want to do it any more. The tipping point for most people is around 45 minutes. Here's a book with a footnote that mentions that the same 45-minute rule applies worldwide and though out history: http://books.google.com/books?id=uuqIA-ce1CoC&pg=PA408&lpg=P...