In a recent article by the NYTimes the openrouteservice API isochrones interface was consumed to derive regions of reachability from subway stations in New York City. Their findings show that two-thirds of 550.000 residents who have difficulty walking live far from an accessible subway station. Head over to this very interesting analysis which you can find here: https://www.nytimes.com/interactive/2019/02/11/nyregion/nyc-subway-access.html
If you are interested to conduct similar studies in your region of interest please feel free to sign up for the free openrouteservice API to make use of a whole range of different services. Our coverage is global for all services which allow you to query up to 2.500 requests per day.
