Moffat Tunnel

How do you model a 6.2 mile long tunnel? More importantly, how do you do it in a compact space?

Construction Photo of the interior of the Moffat Tunnel.

One approach would be to not model it at all. This is the Mike Danneman solution in his layout, where the Moffat Tunnel becomes the entrance to a helix to the staging yard. I considered this solution. However, I really wanted to include Winter Park and either Fraser or Tabernash (if not both) so that I could model the end of the run of the Ski Train. So, I wanted to model the West Portal of the Moffat Tunnel as well.

Another approach would be to use the room, perhaps wrapping the tunnel around the room on a narrow shelf. I considered this, but decided that I could do better. The third option I considered was to use a helix within a helix to provide length while first climbing, and then descending within the ascending helix. Thus, I could have the summit inside the tunnel, while making the elevation difference between the east and west portals only a few inches.

Eastern Moffat Tunnel Plan.

In the plan, the east portal leads to the outside of the helix. The track climbs, spiraling in until it reaches an elevation of 54.25 inches, 4 inches above the east portal entrance. The track levels off for 135 degrees, a length of 46 inches. Then, the track begins to descend on an inner helix. After almost three complete laps, the track emerges at the West Portal of the Moffat Tunnel.

Western Moffat Tunnel Plan. One intermediate lap between the eastern and western parts of the tunnel is not shown in the plans.

The result is a tunnel that ascends four inches, then descends 7.375 inches for a cumulative descent of 3.375 inches. The resulting tunnel is about 50.5 feet long or about 1.5 scale miles. The model representation of the tunnel is about a quarter of the prototype tunnel length. The summit of the tunnel comes to within about 8-9 inches of the ceiling. While I could add additional laps to the helix to climb higher before descending again and lengthen the tunnel, I think this length is reasonably proportional to the other tunnels in the layout. Operating such a long tunnel will be a little discomforting for many engineers, so the helix as is will need to be signaled to inform the engineers of the continuing progress of the trains through the tunnel. Such sensor systems are not unusual in similar applications.

Cameron Turner