As the line southwest of the Amtrak-owned Capitol Hill Tunnel passes among the buildings on the south side of the National Mall, bridging over three streets below, the CSX (ex-B&O) and NS (ex-Conrail, ex-PRR) freight lines join from the east at the signals and junction at Virginia Avenue Tower (CP Virginia, MP 137.1 on Amtrak, whose ownership ends here), and the double track combined routes (now owned by CSX, after more than two decades of Conrail ownership), with supports for the erstwhile PRR catenary to the erstwhile Potomac Yard, bridge over I-95 below, and turn west, with speed limit 40 mph, past two bridge over streets below and the former location of the wye north to the erstwhile 7th Street Station, southwest past a bridge over a street below, Intermediate Signals at MP 111.3 (on CSX), the VRE station with three tracks (the third newly cut-in in 8/07) and two side platforms at L'Enfant Plaza, a bridge over a street below, two bridges/streets overhead, a bridge over a street below, and a street alongside to the north, and south-southwest, past a bridge over a street below, the Jefferson Monument just to the north, a bridge over a street below, and Intermediate Signals at 14th Street, across the three track, through girder, 14th Street Bridge (MP 138.45, when Conrail owned the line, speed limit 45 mph), which crosses both an inlet and the Potomac River, past a CSX detector at MP 110.3 on the bridge, into Arlington (and thus into Virginia) past a signal bridge with Intermediate Signals just west of the bridge, a bridge over the George Washington Parkway and the signal bridge and crossovers at RO (MP 110.0), where a PRR line once turned north-northwest to Rosslyn, south past a VRE passenger station at Crystal City, which has two side platforms and extra track on the west side, and then along the east side of the site, now largely cleared of the former PRR Potomac Yard, where electric locomotives from the north once delivered their freight trains to be switched into ongoing trains for the railroads to the south, past a road bridge overhead, a bridge over a stream below, and Intermediate Signals at xxx Run. Overall speed limits on the double-track, CTC, line south of RO are 70 mph for passenger trains, 60 mph for intermodal trains, 55 mph for manifest freights and light engines, and 45 mph for coal, phosphate and sand & gravel trains. However, all trains are restricted to 40 mph between MP 110 and MP 108.0.
Tracks of the Washington Metro run alongside this line for several miles, past the location where a Southern branch once bridged overhead as the line turns south-southwest, signals where a spur trails in on the east side, CSX detectors at MP 107.4 and/or MP 106.5, crossovers at NA (MP 105.7), where the south end of the yard once trailed in on the west side, a road bridge overhead, two bridges over streets below, and a bridge over a street below just north of the station. At Alexandria (NS MP 8.2/CSX MP 105.2), where the line turns southwest, the Amtrak station (Alexandria Union Station, brick depot on the west side with columns supporting the platform shelter) adjoins a Metro station, on the east side of the Amtrak platforms. All trains are restricted to 40 mph between MP 105.2 and MP 104.8. Immediately south of Alexandria Union Station, there is a road bridge overhead, the line turns to the west, past crossovers at Pepco, a Metro yard on the south side, and the former Southern Seminary Yard on the south side,. and the route taken by the Crescent Limited and the Manassas VRE trains diverges on both sides at AF Tower (NS MP 9.1/CSX MP 104.3)), and then the track on the south side passes under the RF&P line to head west while the RF&P turns again to the south.