Thursday, February 16, 2012

Experiments in mapping transit frequency

A few months ago I spent some time playing with the data released by MassDOT, especially the MBTA schedules represented in Google Transit Feed Specification. I also started collecting data which I summarized in an earlier post about real-time Commuter Rail on-time performance. The MBTA publishes its GTFS data on a quarterly basis, so I downloaded the current version, and ran some queries on it, focusing on a normal working day's schedule.

I'm using the Google Fusion (beta) again. Here we see every MBTA transit stop represented as a marker on the map. I'm using a color scheme where blue represented stops that only average less than one vehicle every 15 minutes (cold), purple is at least every 7.5 minutes, yellow is at least every 5 minutes, and red is better than that (hot!). I'm assuming a 20 hour span of service, so rush hour-only buses do not count very heavily. You can click on a marker to find out what routes stop there, and how many times in a typical weekday.

It should be easy to pick out some of the corridors: Comm Ave, Mass Ave, Washington St (several of them), Blue Hill Ave, etc. The hottest spot is Dudley, as it should be, followed by Forest Hills, Ashmont, and Sullivan.

I was inspired to check out this data while standing around, earlier this week, in Somerville Union Square and realizing that there was not going to be any bus coming for at least 25 minutes -- even though many bus lines connect there. Sure enough, that part of Somerville is mostly blue, except at the very center where the infrequent and rush hour-only buses happen to add up to a yellow dot.

Anyway, I'm still learning how to use the Google Fusion data visualization tool, and hopefully I can come up with some better maps in the future.


  1. Interesting. I never thought of mapping frequency by bus stop rather than by bus line. Maybe not as useful to the transit rider, but good for transit planner, to compare against their data on ridership by stop. It would be interesting to see where that comparison breaks down.

    Could you change your breakdown categories to give more differentiation of the "low-frequency" stops? If a bus comes more than every half-hour, that's pretty good in most places. Also, 10 minutes would be a more intuitive break than 7.5.

    Thanks for the into and happy mapping!

    1. You may want to check out Jarret's writing on this subject,

      Choice of breakdown is somewhat idiosyncratic. I tend to feel that 15 minutes is the break-even point for "show-n-go" transit vs being shackled to a schedule. But some people have a lower or higher threshold. I had to make a tough choice though, because of the limitations of the Google Fusion display: there's only 4 colors.

      The heat map version is somewhat more nuanced, but I couldn't make that work in Google Fusion, so it's just an image file.