All signals within the limits of Washington Terminal Company ownership are color position light (CPL) signals. The station originally used semaphores; they were "modernized" to CPLs at some point in the 1930s or 1940s.
The RS1 was an ALCO-built "road switcher". WTC dieselized with RS1s in 1939, and they were still clanking around the terminal at the time Amtrak took over operation of all non-commuter passenger service in the U.S. During the 1970s, WTC also tested a Romanian-built diesel-hydraulic switcher called the "Quarter Horse". It lasted only a couple of years. In the 1980s Amtrak began replacing the RS1s with somewhat newer end-cab switchers (RS1s have a short hood at one end, long hood over the prime mover). I don't know where those came from.
Ivy City yard is north of the "B&O wye" that connects the Metropolitan Sub to the Capitol Sub, and handles both passenger cars and locomotives. South of the wye is a long service building for Acela Express equipment, and a yard (formerly the commissary yard, exclusively for dining cars) that handles VRE equipment. To the east of the former commissary yard is Washington Metro's Brentwood Yard. The Metro Red Line tracks use the former alignment of the B&O tracks into the station from the west. Close to the station, former platform tracks 1 through 6 have been removed. The Metro tracks are on the far west side, descending into a portal about where the midpoint of the platform for Track 1 would have been. The rest of the area is taken up by a yard for MARC equipment and by some crew buidings.
I don't have any videos for you, but if you visit Washington, book a room in the Marriott Courtyard adjacent to the New York Avenue Metro station, and ask for a room on the east side. You'll have a panoramic view of Union Station's trackage. I'm staying there myself for a couple of days next week.
Randy Resor, aka "NellieBly" passed away on November 1, 2013. We honor his memory and his devotion to railroading at railroad.net.