If you work at Gannett Government Media (née Army Times Publishing Company) in Springfield, Va., you will, from time to time, wait for a pair of rumbling Norfolk Southern locomotives to drag a string of hopper cars across the road and into the nearby concrete plant. It is the train my co-workers and I love to hate.

It eventually occurred to me to wonder what the railroad was doing there in the first place — not the industrial stub, but the main line it connects to. The answer, it turned out, lay some 170 years in the past.

I shared what I’d learned with my colleagues, Pecha Kucha-style:

Production notes: The super-high quality audio was recorded by my iPhone in my shirt pocket while I gave this talk on March 10. Afterward, I exported the slides from Keynote as an M4V file and added the audio in iMovie. Oddly, the video moved more quickly than the audio, but iMovie makes it easy to arbitrarily speed up video clips, and I got them to sync without too much trouble.