It is becoming ever more common for local transport authorities to publish their data on public transport networks in GTFS format. Two of the advantages of so many agencies using a standardized data format is that it makes it easier for us (1) to apply the same research methods to different cities and do comparative studies, and (2) to share our scripts, get feedback and learn from others.
While working on my PhD on transportation equity in Rio de Janeiro, I have written a script in R that converts GTFS data into an igraph so I can run some network analysis. I shared this script on GitHub yesterday and it got the attention of a few people on Twitter, so I thought some of you might be interested as well. Get in touch if you would like to share any feedback or do some collaboration. :)