From Relay, where the original B&O Old Main Line trails in from the west-northwest, along the Patapsco River valley, along the north side of the line, the double track, CTC, line heads east, with speed limits 35 mph for passenger and 30 mph from MP 10.1 to MP 6.7, past former bridge abutments, detectors at MP 9.0, dual road bridges overhead (I-195), a road bridge overhead, Intermediate Signals at St. Denis (MP 6.8), extra track trailing in on the east side, and 50 mph for passenger, 45 mph for freight, on the through girder bridge above the Amtrak Northeast Corridor, and turning north-northeast to a signal bridge at Halethorpe (MP 5.9), where a track trails in on the east side, .
The speed limit drops to 50-40 at BTSC (MP 5.8), past Lansdowne, where there are facilities on the west side of the line, a bridge over a divided east-west highway (I-695), Intermediate Signals, a road bridge overhead, a street alongside to the east, to MP 3.8, and to 45-40 past a signal bridge at West Baltimore (MP 3.2), where the line to Curtis Bay Junction diverges on the west side, a road bridge overhead north of the junction, to MP 3.1, where it reverts to 50-40 edging northeast and then north-northeast again past Mt. Winans Yard, trailing in on the west side, passing under the through girder bridge carrying the Curtis Bay Branch east, with the yard still alongside to the west, past a rail-served facility on the east side, and a grade crossing, and passing above the stub of the Port Covington line.
The line continues north-northeast past a former wye on the west side, a bridge over the Gwynns Falls river, dual wide road bridges overhead (I-95), a road bridge overhead (Monroe Street), and the South Baltimore Industrial Track trailing in from Curtis Bay on the east side (two separate tracks trail in from the east), and two extra tracks on the east side, and turning east, with a spur splitting off on the south side, past a grade crossing (Bush Street) to the crossovers at Carroll (MP 1.5), where the MARC lead splits off on the west side, past a grade crossing (Bayard Street), a signal bridge, a grade crossing (Ridgeley Street), a wide road bridge overhead (Russell Street), and a grade crossing (Warner Street), and turns north adjacent to the Bailey Wye, where a line continues dead ahead and the CSX Freight Main Line, on the east side, also turns north, past a road bridge overhead (Ostend Street), the east leg of the wye trailing into the freight tracks, the Light Rail tracks on the east side, a footbridge overhead to the Ravens' stadium, the freight line separates to the east side, and a road bridge overhead (Martin Luther King Jr. Boulevard), to enter the terminal platforms (east side and center 'island' on three stub tracks) at Camden station, with speed limit 45-40 to MP 1.2, 30-25 to MP 0.5, and then 15 mph the end of the terminal tracks in the rump of Camden station (somewhere before MP 0.0, with the portable buildings that now comprise the station facilities just to their north).
The speed limit on the freight tracks on the east side is 25 mph from MP 1.5, past the wye with the Locust Point Branch, on the east side at Bailey (MP 0.7), where the, now single track, main line turns north alongside the MARC leads, past HB Tower (MP 0.4/96.0), into the Mount Royal Tunnel and beyond.