It is a question that can be answered by using the service Mapnificent, which enables users to create isochronics maps from the website using opened data or shared datas provided by transit operators and cities.

What is a isochronics map ? A map visualizing the different areas you can access given a certain amount of time. Some touristic rough guides have been using it, to inform their reader about how to travel through a city or a region in a certain window of time. 

On Internet, the open data policy from transit operators or cities is a deep change that can help adress and challenge the "accessibility" of urban environments and provide new ways to read the cities. 

On Mapnificent you can cross datas with specific search from starting points, arrival points or interest points

we were curious to compare Boston, New York, Los Angeles and San Francisco, between public transport oriented cities ou "car cities", those screen shots from the service below all have the same time unit of 15 minutes to compare their area of accessibility by public transport.

In France, it is Bordeaux and Rennes cities which are available on the service for the moment, having opened their datas. Check out a range of various cities around the world using their service and play comparing them ...

credits : screenshots from http://www.mapnificent.net/ created by Stefan Wehrmeyer.