Into the Tunnels: Tunnel 1

The Moffat is known for the tunnel district. Between Denver and the Moffat Tunnel, a distance of 50 miles by rail, there are 28 tunnels. These are clustered in a span of 17.3 miles, starting with Tunnel 1 (MP 23.2) and ending with Tunnel 30 (MP 40.5). (Note that Tunnel 9 and Tunnel 28 no longer exist.) This series of tunnels and the regions through which they take the Rio Grande is one of the major reasons for my interest in the line.

Caboose 01460 rolls by while a gaggle of SD45s pulls the train into Tunnel 1 on the far side of Coal Creek Canyon. Photograph by Chuck Conway.

The tunnels at the ends of the district are orphans. They are different from the rest of their siblings. Tunnel 1 allows the main line to withdraw from its first encounter with the front range and retreat to climb along the Flatirons that make up this barrier. Indeed, there are 2 miles between Tunnel 1 and Tunnel 2. Furthermore, one could also argue that it is a full 3.5 miles before the railroad once again tries to thrust its way into the mountains like it does in Coal Creek Canyon. Tunnel 1 is a prologue to what is coming, and Tunnel 30 is a reminder of what the railroad has gone through to get there.

Tunnel 1 is 299 feet long, or 22 inches in N-scale. Indeed, it could be modeled in full scale at that size. However, as I worked on developing track plans to model the tunnel district, I found that while some tunnels could be modeled at scale (Tunnel 29 is only 78 feet long), others would be challenging (Tunnel 17 is 1730 feet long). Early on, I adopted a goal to model the tunnels using a formula so that the shortest tunnels would be full scale, while the longest tunnels would be shortened to something more reasonable. Using this formula, I established the following goals for modeling each tunnel, as shown below.

Table of the actual versus target design lengths for the layout tunnels.

I am pleased to note that the median (0.84) and average (0.83) compression ratios are very similar. Furthermore, the target tunnel lengths all maintain the rank ordering of tunnels in terms of their length. Several tunnels (4, 7, 22 and 29) have little or no compression, while the longest tunnels (10, 17, and 23) all are much more palatable in terms of length. For instance, tunnel 10 would be 117.9” long at full scale, but its target design length is now 75.46”. At a little more than 6 feet long, that is still a long tunnel, but many trains will still be long enough to be visible while in the tunnel. If modeled to full scale, that would not be the case. Yet, a six foot tunnel still garners the feel of an immense tunnel.

Tunnel 1 is the first tunnel to transverse a sand and pebble conglomerate that forms the backbone of the flatirons. The flatirons are up thrust sedimentary slabs that form a picturesque backdrop to Boulder, Colorado. The railroad east and west portals are both concrete with sprayed concrete and gunite added in between to maintain the stability of the tunnel. The exterior of the rocky outcrop through which the tunnel passes is dotted with ponderosa pine trees. Based on the target length for Tunnel 1, the model should be approximately 20 inches in length, about 89% of the full-scale tunnel length but still substantial. 

Plan for the Tunnel 1 area.

Just to the railroad west of Tunnel 1 is a grassy area where the mainline curves around as it prepares to swing around to the north and enter a flat spot known as Plainview. I positioned Tunnel 1 to allow for this curve while achieving the target design length of 20" which works out to be about 267 scale feet. This is very close to the target length. This last stretch of main line also brings to an end the steepest climb on the railroad. Just as on the real thing, the main line grade moderates at Plainview as the line enters Plain Siding, but more on the design of Plainview in another post.

Cameron Turner