I love data-driven bug hunts like these and like the classic 500-mile email.
Especially when they're transit-related. I once spoke to someone from the Dutch railway agency. They had a weird peak in their train data at Amsterdam Airport around 2-3am almost every weekend. Turns out that hungry partygoers in Amsterdam took the train to the airport to go to the Burger King there, the only fastfood place that's open until 4am.
I really emplore you to find some open data and just set your own challenges. I did that with Citibike open data and that snowballed into a 300-line 17-hour script that won me a trip to California. I've never heard the term Marey Chart, even though I'm now doing my third course related to railway transportation. We just call them time-space diagrams or blocking diagrams if they include the train's block occupancy times, like this visualization I made in Matlab a month ago:
I messed with the TfL APIs a little bit, they're pretty good. But that was more of a software development exercise when I was job hunting: http://rjw-tfl-bikes.herokuapp.com/ (this just plots the locations of bicycle hire on a map). Fine, I'll have another look. Maybe the fact that I can share it on here will motivate me... I didn't know the name either, just seen them referred to with regard to Tufte.
I also had some fun with the TfL API, mostly to get my foot in the water regarding GET requests / REST services / XML. Try to find a big spreadsheet and try to prove/disptove a hypothesis, or visualize the data in a new way. Here, check this out. Let me know what you come up with! :)