This was originally a final project for my web development class, but I took it much farther than was required.
Let’s go over the functionality, and then I’ll dive into the implementation.
Here is a link to the page, so you can play around with it. Unless it’s daytime PST, you probably won’t see any buses.

The map shows the live location of all buses currently on the road. You can use the sidebar to filter out bus routes you don’t care about. Clicking on a bus toggles the route it is following being drawn on the map. Clicking on a bus stop gives you directions to it from your current location, as well as showing a list of buses that are scheduled to stop there soon, and how delayed they are.

Originally we were supposed to build some rudimentary functionality by divining how Spokane Transit Authority’s (STA’s) API worked for their unreleased route planning site by monitoring network requests. But their API sucks. Or at least it did at the time. So I did a little digging and discovered that public transit providers around the world use something called The General Transit Feed Specification (GTFS) which is made by Google. There is also GTFS-R which is the real-time variant. STA had set up their own transit feed loosely following this specification and exposed the data in it through their REST API. I could also access the feed directly via some *.pb files on STA’s site. However, when you opened it, it looked basically like random binary data.

Thankfully, Google has GTFS Realtime Bindings on GitHub. Now instead of figuring out how to work STA’s clunky API, I could pull some of Google’s code, and extend it into a REST API of my own to use on the project. Google provided some PHP code that downloaded the latest pb file from the GTFS-R feed and parsed it out in a slightly usable, poorly documented PHP object. I spent a few hours poring through the several thousand line PHP file boiling it down into something I could actually comprehend (doc1, doc2). I then turned the entire PHP object into an associative array that could be easily encoded as JSON. I also implemented some caching so I wouldn’t be putting to much strain on STA’s servers.

As the front end progressed, I would break off the pieces I needed into an endpoint.

Some run of the mill Google Maps API documentation/tutorials later and I had a functional (and useful!) client and server.

Source Code