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GTFS Data Exchange
GTFS Data Exchange is a site where public transport data schedules are uploaded in a uniform format which can then be used by developers.
GTFS stands for General Transit Format Specification, and seeks to be a universal file format for transit data. The starting G originally stood for Google, the company that created the format, but this was changed to general in early 2010. 
The GTFS Data Exchange is a website that stores data uploaded by public transport data holders, to allow it to be easily developed. There is an RSS feed for each supplier of data so a concerned developer can be alerted as soon as newer data is available.
As well as the public transport data itself, the site also says whether or not the information is from an official source and when it was uploaded to the repository.
The transit data is free for anyone to download and use.