Every bus should have a GPS transmitter, and its transmissions should be uploaded to Google Maps through a standard API which could be used by all transit agencies in the nation. Every bus in the nation should have a unique ID that would identify the route number and transit authority/system that each bus is a part of. The system should be smart enough to support light-rail systems, ride-sharing businesses, and perhaps regional and national carriers like Greyhound as well.
I should be able to pop up Google Maps on my smartphone in any city in the nation, and see where the next bus actually is, how long it will take to reach me, where it goes, and how it can connect to other nearby transit systems.
On the back-end, Google trip planner could use this real-time data to update its transit maps in real-time, giving me up-to-the minute directions on how to get from Point A to Point B.