As several readers have pointed out, there's a pretty much up-to-date track map available on the IRM website, and I thank you for the reminder. But at IRM, yesterday's news is already obsolete.
Pete Schmidt, long-time IRM member and friend, has sent me a newer version. The new cutoff and Yard 15 track are shown outlined in green. Both of these tracks are now essentially complete and are being fine-tuned. Pete lives in Baltimore, and has done a fantastic job of track-mapping museums all over the country.
I should point out, however, that Barns 13 and 14 are not yet under construction, really, and Yard 13 is not yet complete. But maybe tomorrow.