Henryton Tunnel

The Henryton Tunnel, located near Henryton in southern Carroll County, Maryland, is the third-oldest tunnel in the world that remains in active railroad use.^[2] Constructed by the Baltimore and Ohio (B&O) Railroad and opened around 1850, it was the first tunnel constructed on the B&O's Old Main Line. In 1865 the tunnel was widened to accommodate double track. It was rebuilt into its current form in 1903. The tunnel has brick portals and lining. The coping and footings are concrete.^[1]: 452

Henryton Tunnel

East entrance to the tunnel. B&O widened the tunnel for double track in 1865, but converted the entire Old Main Line to single track in 1959, to utilize higher center tunnel clearances.[1]: 174
Overview
Line	Old Main Line Subdivision
Location	Henryton, Maryland
Coordinates	39.3512°N 76.9128°W / 39.3512; -76.9128
System	CSX Transportation
Start	Near Marriottsville, MD
End	Henryton
Operation
Constructed	1849-50
Opened	1850
Rebuilt	1865, 1903
Owner	CSX
Traffic	Train
Character	Freight
Technical
Length	430.4 ft (131.2 m)
No. of tracks	1
Track gauge	1,435 mm (4 ft 8+1⁄2 in)
Width	30 ft (9.1 m)

See also

• Baltimore and Ohio Railroad
• Industrial Archaeology