[soapbox] Here's the deal. It's a model railroad. Which means it works like a railroad, but it looks like a model. While some of you might get your rocks by modeling the 150 scale feet of actual proto paradise most of us have room for, that's not going to work for me.
I want my trains to originate someplace, pass through several representative vignettes, maybe do a little work along the way, then head off into the fifth dimension to their destination. I want the types of traffic carried to be representative of my prototype, and same for the engines, rolling stock, and structures.
Tunnels are a necessary evil to create these representative scenes. The good news for me is that my chosen prototype liked drilling more than Tiger Woods and BP combined! Five major tunnels between Hagerstown and Cumberland, three on the Connellsville line, and even one between Blue Ridge Summit and Gettysburg for good measure! And if you throw in trackage rights, you can even count B&P and Union Tunnels in Baltimore.
The cool thing about using tunnels creatively is you can have a train exit a scene depicting a bucolic river crossing, and have it emerge 100 miles away in a big city in the space of a few feet. It's a major enhancement to the "play value" of a model railroad. And if your clever enough to provide for a little access from below or behind the scenery, it's not that big a deal to take care of. [/soap box]
Lee