GTFS has helped the transit industry begin to develop a “stack” of layered services. In computing, a software stack or solution stack is the set of systems that create a complete platform to run applications. We have begun to see the emergence of a transit stack.
In order to describe and explore this, I created a diagram, below. The goal is to show transit technology as a modular system.
Note that only some of these functions have standard interfaces to be connected together, such as GTFS-realtime and GTFS. Many of the unlabeled lines and arrows represent additional need for standard data formats and interfaces. To the extent we develop standard interfaces, it will make systems more modular, less costly, and less risky to implement.
This is an early draft diagram. Comments are welcome! Feel free to share with attribution to Trillium. Link: Google Docs