I’m looking for a way to retrieve or compute a congestion index for a whole city with the Traffic API.
Does anyone have a clue about that?
It might be hard to do it with a standard Traffic API. You would have to perform a lot of API calls to get the most data out of it, then analyze it and compute the approximate congestion index. Maybe you can take a look at the Traffic Stats APIs? It requires a custom agreement, unfortunately, but maybe it will help you with solving your issue…