From Googling around it looks like the best way to build an Arduino project using GTFSR is via an intermediary device that converts the GTFSR to JSON or other. Would it even be possible to do it all natively on an Arduino or similar?
-Alastair
Assume you have seen this article Catching The Bus From My Living Room | by Ian D. Westcott | Medium which sounds similar to what you are doing. Seems as if getting it natively is impossible…
But will leave it to the more intelligent folk on this forum to advise!
Yea, that medium.com link is like many others where there is basically another device in the mix… surely there is a way to do it on Arduino only. I think the approach would be to parse in real time and treat it as a state machine (not storing anything along the way since there is so little memory). I just don’t have the skillz/time to do it. 
There does not appear to be a native C binding for GTFS Realtime so thats the problem and why people use an intermediary device to do the conversion.