I am on a committee looking to redesign transit service in Sacramento and need to be able to make equal-time maps or "isochrones," like the attached. A prominent difference between transit isochrones and road isochrones is that each transfer has a temporal penalty. That is, it takes time to wait for the connecting bus. Also, that penalty is lower where the connecting routes are more frequent and higher where the connecting routes are less frequent. Also, some routes only serve stations, while others are considered to have a even distribution of stops along their routes.

(If you are interested in why I want to be able to generate isochrones: I am interested in a hybrid model between frequency and coverage that still creates a high-frequency grid between major traffic generators, but with routes that take different branches between the generators. This offers both frequency and coverage. Currently, the debate is binary, frequency or coverage.)


[![Transit Isochrone Example][1]][1]


  [1]: https://i.sstatic.net/g3crX.png