This project was motivated by a very simple problem: I want to take a day trip to Providence. When should I leave and come back?
Agency timetables aren't too helpful for these types of situations because one would have to cross-reference numerous routes' tables, depending on a particular start and end -- especially if your itinerary requires a few transfers. Map-based applications like Google Maps are OK, but really I care much less about the map and much more about the timetable.
In essence, this turned out to be a design problem. How do you display a potentially very large amount of time information in a usable, readable, searchable fashion?