The Othello Tunnels on the Kettle Valley Rail Trail
There are a lot of trails with one or two tunnels on them, even a few with more. But there are few trails with a lot of tunnels and some others that could have a s---ton of tunnels (trying to keep this family friendly, but as a women I used to work with would say "a s---ton is a great term of measurement. Everyone knows that all you ever need is one s----ton. No one ever says we had two s---tons of something."
The North Bend Rail Trail in West Virginia has 10 tunnels, including a few of the longer ones in the country, and so does the Route of the Hiawatha Trail in Idaho, including the 2nd longest bike tunnel in the world. The Milwaukee Road Rail Trail, also in Idaho has 9 - and it connects to the Route of the Hiawatha, because both were built on the old Milwaukee Road. The John Wayne Pioneer Trail (aka The Iron Horse Trail) in Washington has 8 tunnels and is also on the old Milwaukee Road. Of course, these are all topped by the Kettle Valley Rail Trail just over the border in British Columbia, Canada - it has 12 tunnels (though if pride is on the line, they're pretty short and there are fewer feet of tunnel on the Kettle than on the North Bend, John Wayne or Route of the Hiawatha). And that's it for trails with 5 tunnels or more.
There are a few - very few - opportunities for such trails.
There's the Fairmont Branch in West Virginia, which was mentioned in the previous post in this series.
A much more difficult lift, with many more tunnels, are the old tunnels in KY and TN on the CN&TP. This line was called the "Rathole" because of it's 27 tunnels and ran from Danville, KY and Oakdale, TN. The primary difficulty here is that while the tunnels were abandoned, the rail line wasn't meaning a trail would need to run adjacent to the rail where the sections weren't bypassed. 5 tunnels are right next to the existing railroad and likely unusable. Furthermore, 5 of the tunnels were daylighted and 1 had a stream rerouted through it. But the other tunnels could be used by a series of trails of varying utility. Tunnels 7-9 are already part of the Cathy Crockett Trail in Kentucky and that trail could be extended to include tunnel 5. The other tunnels are on one of 7 bypassed sections, but none of those sections would use more than 3 tunnels.
Another multi-tunnel rail line is actually in the process of being made into the trail. The Rock Island Trail will stretch over 200 miles across the state of Missouri and include 4 tunnels with a total length of over 4000 feet.
Some of the trails mentioned above could have other tunnels added. The North Bend Trail passes by two bypassed tunnels that could be added - at least as hiking detours. The Kettle Valley has more tunnels than are on the trail - but I'm not sure how many as the documentation on it is lacking. It seems Canadian rail fans aren't as rabid as American ones.
But the big opportunity is the Milwaukee road. Much of the western end of the Pacific Extension, a line from Minneapolis to Seattle, was abandoned in 1980 and parts of that have been transformed into six rail trails in Idaho, Montana and Washington using 28 tunnels. The abandoned section starts in Terry, Montana and is abandoned almost the whole way to Renton, WA, but for a small section near St. Maries, ID - a section that can be bypassed using another rail trail. Altogether it's about 1100 miles. A trail along the whole right of way, connecting all the existing trails, would pass through 46 tunnels. It would be by far the longest rail trail in the world, with the most tunnels, pass through some amazing country and provide access to dozens of cities and towns including Seattle and Butte - and that's without counting all the spurs. Maybe someday.