More roads or public transit? Insights from measuring city-center accessibility

We propose a theory-inspired measure of the accessibility of a city's center: the size of the surrounding area from which it can be reached within a specific time. Using publicly-available optimal routing software, we compute these "accessibility zones" for the 109 largest American and European cities, separately for cars and public transit commutes. Compared to European cities, US cities are half as accessible via public transit and twice as accessible via cars. Car accessibility zones are always larger than public transit zones, making US cities more accessible overall. However, US cities' car orientation comes at the cost of less green space, more congestion, and worse health and pollution externalities.