In regards to the GTFS-realtime feed. I've seen the following at the top of the Feed Entities section on GTFS.org.
"GTFS Realtime supports four distinct types of realtime data, that can be combined witin a single realtime feed. Summaries are given below, with full documentation given in the relevant section."
I'm curious how common it is to provide a single merged feed of all feed types, and if Google and other 3rd party consumers support a merged feed.