"How likely is it that the arrival and departure information will be available on a site or service other than the official one? That depends on how open your local agency is. In some metro areas, transit agencies make data--routes, schedules, and even real-time vehicle location feeds--available to developers to mash into whatever applications they wish. In others, the agencies lock down their information, claiming it may not be reused without permission or fee."
New York's MTA is claiming copyright over its data. San Francisco is now writing data accessibility into its contracts. Portland is the most open of all.