GTFS-RT data isn't a lot of fun to work with directly, though, so I'd recommend that you use an intermediary like OneBusAway (OBA) to interpret the data and give you a nicer to use API.
I thought about this, but I've seen several times where the signs say that the train is running late, but it's actually there and leaves perfectly on time!
The schedule has been much more reliable since the electrification
I've explored this--you need 511 API access to obtain real-time data, and to conceal your API key you need to stand up a web application.
Cool proof-of-concept, need to take it to the next level!