As noted last week, there are quite a few trail tunnels in the area, including some of the longest in the world. Looking at the four closest states to DC and DC, the number of bike/ped tunnels are pretty impressive:
DC - 2
Maryland - 9
Virginia - 11
West Virginia - 18
Pennsylvania - 17
But there are still plenty of abandoned railroad and highway tunnels in the area that could be be made into trails or parts of trails.
Here, for example, are the longest abandoned tunnels in the area, in order
- Big Bend Tunnel, WV (6500 feet) - famous for the Ballad of John Henry
- Laurel Hill Tunnel, PA (4541 feet)
- Knobley Mountain, PA (4408 feet)
- Blue Ridge Tunnel, VA (4264 feet)
- Gallitzin Tunnel, PA (3612 feet)
- Koontz Tunnel, WV (3164 feet)
- Lodgeville Tunnel, WV (2708 feet)
- Chapline Hill Tunnel, WV (2500 feet)
- Dupont Circle Streetcar Tunnels, DC (2400 feet)
- Lough Tunnel, WV (1517 feet)
Most of these aren't likely to be trail tunnels.
Big Bend, Lodgeville and Gallitzin tunnels were abandoned, but the railroads were not and now pass through parallel tunnels and so the railroads would surely frown on their adaptive reuse (which would have little utility as well). The Laurel Hill Tunnel which, like the Sideling Hill and Ray's Hill tunnel is an old turnpike tunnel, is currently being used as a test track for race cars. And the Dupont Circle Tunnels (above), as much as I'd like to see the west one turned into a "high line" style facility allowing for through bike/ped traffic (I mean seriously, it would be awesome), are unlikely to ever be reopened for transportation.
But several of the others have real possibilities.
Knobley Mountain Tunnel is part of an 6 mile long, out-of-use railroad from Pinto, MD across WV to the Potomac at Patterson Creek. There's already an effort to turn the Blue Ridge Tunnel into part of a trail, with Nelson County, VA amending a bid for restoration work as was just reported today.
“If this works, which hopefully it will work, the tunnel itself will be substantially restored and rehabilitated, and then we can aim at the third and final phase, which is the trail and the parking lot. The progress is slowly being made,” Carter said during the board meeting.
The Koontz Tunnel, and the shorter 942-foot long Carnifex, are on the same rail line as the Meadow River Rail Trail. Though there's not a lot of clear indication about the plans to take that north to the Koontz tunnel, this map of proposed trails does show the trail going through it. It would presumably bypass the Carnifex which the NPS closed in 2014 for safety reasons.
The Chapline Hill tunnel under Wheeling, WV might someday become part of the Wheeling Heritage Trail; and the Lough Tunnel could become part of an 8-mile long rail trail but it doesn't appear to be on anyone's plans - probably because the whole coal mine spur is kind of in the middle of nowhere (see below).
In addition to these long tunnels, there are a few abandoned lines that offer opportunities for multiple tunnels.
At the top of this list is the Farimont Branch in WV. The 65 mile long railbed extends from the Monongahela River in Fairmont all the way to the Ohio River in Moundsville, and it passes through 5 old tunnels along the way, the longest of which is the 1250 foot long Welling tunnel. A couple of sections, in Hundred and Mannington have been turned into short trails (the East Wetzel and the John McCann Memorial respectively) but together they account for less than 4 miles. There are plans to extend the McCann east, but not to build out the whole ROW, which is too bad since it would make a great addition to the Industrial Heartland Trail system.
Another one is the the B&O railroad's Wheeling Pittsburgh Subdivision between Washington, PA and Wheeling, WV. The west end of this line is part of the previously mentioned Wheeling Heritage Trail, but the rest of the line would make a great extension passing through numerous towns along I-70. It has five tunnels on it, all in Pennsylvania, with the longest being the 1052 foot long Finney Tunnel.
There are some smaller ones too. The abandoned 17 mile long Bluefield Subdivision from Pocahontas to Weyanoke in WV has a pair of short tunnels just south of Rock. There are a couple of other tunnels (Top Mill and Mt. Wood) in Wheeling that are planned additions to the Wheeling Heritage Trail.
A little closer to DC, there are three long tunnels that were to once be part of the Western Maryland Rail Trail (the Kessler, Stickpile and 4350 foot long Indigo) but they were closed by the NPS so that they could be bat habitat instead. But, the much shorter (~100ft) long Pleasant Plains Road Tunnel will be part of that trail's phase IV which is currently underway.
In the immediate area, trail users might someday ride through a replacement for the Air Rights Tunnel along the Capital Crescent Trail in Bethesda and through the Union Market tunnel under New York Avenue in DC. The first is very likely, the second, very unlikely.