"AllTransit is a proprietary dataset we created to measure transit access and connectivity across the United States. It was developed to rapidly create new GTFS data and easily import and normalize publicly available GTFS data.
In addition to the publicly available GTFS data provided by transit agencies, we have created GTFS structured datasets for all major agencies in regions with populations greater than 250,000 as well as a large number of smaller regions and agencies. AllTransit has station, stop, and frequency data for bus, rail and ferry service for over 500 agencies."
Text from: http://www.cnt.org/tools/alltransit