On your MARC! - Okay…bad pun…on to the caption. - With a day to kill I hopped on Acela Express 2160 out of D.C. and got to Baltimore late morning. After exploring and shooting the splendid Penn Station I headed out on foot to see what was easily available. I hadn't realized how accessible the famed B&P Tunnels were just to the south of the station. I shot two Acelas and an Amtrak regional before finally getting this southbound commuter. This shot looks down from the Howard St. overpass at a departing Washington, D.C. bound "Penn Line" run being pushed by one of MARCs sharp looking new MPI built units. The tunnel was constructed by PRR predecessor Baltimore & Potomac Railway and was opened for business on June 29, 1873. The 7,669-foot bore (broken up by two short open cuts) sits on a 1.34% grade and is arguably the biggest bottleneck on Amtrak's entire Northeast Corridor with a speed restriction of 30 MPH due to curvature. To the right under the large stone arch of the North Ave. bridge lead the rails of the old Northern Central Railway (a PRR subsidiary) which served as a through route between Baltimore and Harrisburg from 1858 to 1972. Today the line extends only a short distance beyond the overpass to reach NS's Flexi-flow terminal. From that point north about 13 miles the line has been reconstituted as a light rail route with NS providing freight service as needed at night. Railroad history abounds in the northeast and despite all that has been lost there is still much to enjoy if you take the time to look. For example, I was pleased at the abundance of former PRR Position Light signals guarding the mainline approach to the tunnel. Speaking of history, I know the old B&P tower is long gone, but there was a small single level building clearly of railroad origin to the right of tracks tucked up hard between the river and the rails. The little structure can be seen in the middle right of the image at the lower right end of the visible stone arch.Does anyone know what it is or was?