This is really cool; a few years ago I wanted to do this for the published schedules of NYC's subway. At the time it involved scraping schedules from the MTA website's horrendous HTML, but now it looks like they've completely reversed direction and have it in an accessible format. Interestingly, they have real-time data for buses, but not for the subway.
On the subway, it's probably harder to get data to the TVS since it would be transmitting from underneath tons of concrete. They could tie it into the train control system, but they probably don't want to connect that to the Internet to prevent the case that someone could take it over and mess with the subway.
