If you were in Denver this weekend, you might’ve seen an unusual sight: A MARC commuter rail train parked behind Denver Union Station.

MARC in Denver. Photo by Ryan Dravitz.

What gives?

Turns out the train was in Colorado as part of the testing for MARC’s new locomotives. Officials wanted to test the new locomotives with actual MARC rolling stock, to evaluate how the locomotives performed in real-life conditions.

The Federal Railroad Administration has a test track in Pueblo, CO, so off this train went.

The train was in Denver because Amtrak carries the equipment on a regularly scheduled train from Denver to Chicago (#5, the California Zephyr) and then from Chicago to DC (#29, the Capitol Limited).

Thanks to Matt Johnson and Twitter user @kencon06 for helping to solve this mystery.

Cross-posted at BeyondDC.

Dan Malouff is a transportation planner for Arlington and professor of geography at George Washington University, but blogs to express personal views. He has a degree in urban planning from the University of Colorado and lives in northeast DC. He runs BeyondDC and contributes to the Washington Post .