The University of Michigan runs a service called Magic Bus which lets users track the UMich bus system in real time. You can pretty easily find and reverse-engineer the XML file that powers the site, and armed with that data you can build whatever you want. I built, several years ago, a service you could text to find out when your bus would arrive.
For research and reference (to see what bus routes disappeared at what times and what error states the system exhibited), I set up a script in 2010 to pull down a copy of the Magic Bus XML data every 15 minutes or so. I found this archive while cleaning off an old server recently, and I thought it might be interesting/useful to throw it online and see what people do with it.
So, here you go: 1.5 years (June 2010 - January 2012) of UMich bus data. Not quite “big data”, but maybe “medium data”? Have fun. Let me know what you do: @cdzombak.