Trail rail trail Fort McHenry Tunnel, quad tunnels, Interstate 95 under Baltimore Harbor, Baltimore Henryton Tunnel, rail tunnel, c. 1850, CSX (formerly Baltimore and Ohio Railroad), west of Marriottsville Howard Street Tunnel, rail tunnel, c.1895, CSX (formerly Baltimore and Ohio Railroad), Baltimore Ilchester Tunnel, rail tunnel, c. 1903, CSX (formerly Baltimore and Ohio Railroad), east of Ellicott City Jones Falls Conduit, water tunnel, built in 1914 to contain Jones Falls (river), from North Howard Street to East Baltimore Street, paralleling Jones Falls Expressway, in Baltimore Paw Paw Tunnel, abandoned canal tunnel, in use 1850–1924, , Chesapeake and Ohio Canal, Allegany County, Maryland, across the Potomac River from Paw Paw, West Virginia, now a rail trail; through same ridge as Kessler Tunnel (Western Maryland Railway) and Graham Tunnel (CSX) Union Tunnel, twin rail tunnels, Amtrak (formerly Pennsylvania Railroad), under Hoffman Street between Greenmount Avenue and Bond Street, Baltimore (three) Western Maryland Railway tunnels, abandoned rail tunnels, in use 1906–1975, Western Maryland Railway ; from east to west: Indigo Tunnel, abandoned rail tunnel, in use c. 1906–1975, northeast of Little Orleans Stickpile Tunnel, abandoned rail tunnel, in use 1906–1975, Green Ridge State Forest in Allegany County, between Little Orleans, Maryland and Paw Paw, West Virginia Kessler Tunnel, abandoned rail tunnel, in use 1906–1975, Green Ridge State Forest in Allegany County, northeast of Paw Paw, West Virginia; through same ridge as Graham Tunnel (CSX) and Paw Paw Tunnel (Chesapeake and Ohio Canal) Massachusetts Road tunnels connected to the Big Dig project in Boston: Callahan Tunnel/Sumner Tunnel, twin tunnels, State Route 1A, under Boston Harbor Callahan Tunnel, State Route 1A northeast-bound only, under Boston Harbor Sumner Tunnel, State Route 1A southwest-bound only, under Boston Harbor Fort Point Tunnel, twin tunnels, Massachusetts Turnpike/I-90 under Fort Point Channel, Boston Ted Williams Tunnel, twin tunnels, Massachusetts Turnpike/I-90 under Boston Harbor Thomas P. O'Neill Jr. Tunnel, twin tunnels, 2003, I-93 (in coordination with the Dewey Square Tunnel), Boston Dewey Square Tunnel, southbound I-93, southbound portion of the Thomas P. O'Neill Jr. Tunnel, Boston Massachusetts Bay Transportation Authority tunnels in the Greater Boston area: MBTA Blue Line rail tunnel: East Boston Tunnel, rail tunnel, between Airport Station and Bowdoin, now part of the MBTA Blue Line MBTA Green Line rail tunnel: Tremont Street Subway, rail tunnel, between Science Park and Boylston, now part of the MBTA Green Line MBTA Orange Line rail tunnels, north to south: Haymarket North extension,