Speaking from my experience in the Northeast US, most cities are still pretty flat. Washington, Philadelphia, New York, and Boston could all be very cycle-able

Speaking from my experience in the Northeast US, most cities are still pretty flat. Washington, Philadelphia, New York, and Boston could all be very cycle-able with the right infrastructure in place. A bit cold in the winter, but nothing unbearable. Suburbs are a bit hillier, as are cities on the West Coast, but even just by selecting for the flattest/most temperate places in the US and building up solid cycling infrastructure, you're still talking about something thats affecting potentially 10's of millions of people.