Remember this map?
I used it in the earliest days of this blog, and it's in almost every presentation I do. It's from a tool that allows you to select a location in a city and see blobs (technically isochrones) showing the area you can get to in a fixed amount of time using transit plus walking. This one is for 9:00 am and the three shades of blue represent travel times of 15, 30, or 45 minutes. In essence, the software takes the point you select and runs the equivalent of Google Transit trip planning searches to find a points where the travel time crosses the threshold; these become the boundaries of the blobs. (For details behind this crude summary, see Aaron Antrim's comment on this post.)
I call this a map of your freedom. It's useful for two potentially transformative purposes:
- Helping people and organizations understand the transit consequences of where they choose to locate, and thus to take more responsbility for those consequences. This, over time, can help people who value good transit to locate where transit access is good -- something that's very hard to discern from a typical bus map but that becomes very obvious here. You can even assess access to specific things that you value, based on exactly where the blobs are.
- Helping people visualise the benefit of transit -- access to your city -- as a freedom, and thus to understand more clearly what transit does for them. It broadens the narrow notion of travel time -- which is often understood for only one typical trip -- into a picture of your possibilities as a transit rider. The percentage of a city's resources (jobs, housing, retail etc) that is in the blobs for a particular location could also form the basis for a meaningful Transit Score that could replace the technologically biased scores now used by WalkScore.com.
The original tool is a beta buried deep in WalkScore's archives. It's basic and very, very slow.
The other main alternative is mapnificent.net, by Stefan Wehrmeyer. Available for many cities, Mapnificent.net looks good ...
... except that it contains two fatal assumptions:
- Initial wait time is excluded.
- Some timing of transfers is assumed, based on the author's experiences in Europe. So he uses an average transfer wait time of 1/3 of the headway instead of 1/2 of the headway, which would be appropriate for random transfers.
Here's the problem. Both assumptions mean that Mapnificent's assumptions undervalue frequency and overvalue vehicle speed. Since this conceptual bias is already very, very common (see Chapter 3 of my book), Mapnificent is seriously misleading in a way that can be really unhelpful. For cities that I know, especially area with lower frequency service, Mapnificent wildly overstates the convenience of transit, and fails to show how locating on frequent service will get you better access to the city.
In my network design course we talk about this. When figuring travel times in the course, I insist on using 1/2 of the headway as the intial wait time and the same as the transfer time (unless there's a pulse) so that frequencies weigh heavily into true travel times, as they do in life. This sometimes sounds silly: If a route runs once an hour does that really mean I wait an average of 30 minutes? Or do I just build my life around the schedule? I view the two as the same thing, really. We're not describing literal waiting so much as time when you're in the wrong place. We're describing the difference between when you need to arrive and when you can actually arrive. This could take the form of arriving at work 29 minutes earlier than your shift starts -- consistently, every day. Effectively, you end up waiting at your destination.
So there are a range of judgment calls to be made in designing these things, but it's worth getting it right because the potential utility of this tool is so significant. The good news: I'm involved with people who are working on something better. Stay tuned!