First Street Tunnel

The First Street Tunnel is a two-track, soft-earth tunnel built between 1904 and 1906 by the Washington Terminal Company to serve as the southern approach to Union Station in Washington, D.C. Currently owned by Amtrak, it connects to lower-level tracks and platforms at the station, passes under Capitol Hill and connects to the RF&P Subdivision (CSX Transportation) and Long Bridge, offering through railway service to Alexandria, Virginia, and points west and south. Unlike the Northeast Corridor tracks north of Union Station, the tunnel tracks are not electrified, so southbound trains leaving Union Station must switch to diesel locomotives before entering the tunnel. Exiting Union Station, the tunnel runs due south under First Street NE and SE before curving to the southwest under a parking lot near the Capitol South Metro station. Its southern portal is just east of South Capitol Street at the intersection of D Street SE and New Jersey Avenue SE.

First Street Tunnel

The south portals in 1999.
Overview
Location	Washington, D.C.
Coordinates	38.88485°N 77.00755°W / 38.88485; -77.00755
System	Amtrak
Operation
Constructed	1904-1906
Opened	1906
Owner	Amtrak
Traffic	Train
Character	Passenger
Technical
Length	4,033 ft (1,229 m)
No. of tracks	2 single-track tubes
Track gauge	1,435 mm (4 ft 8 1⁄2 in) standard gauge
Lowest elevation	63 ft (19.2 m) below street
Tunnel clearance	17 ft (5.18 m)
Width	Each tube 16 ft (4.88 m)
Grade	0.13%

The tunnel's height is 17 feet (5.2 m).[1][2]