A Junction and a Helix

In the last post, I described my space and provided a conceptual benchwork configuration for my proposed layout. This post begins the description of the track plan for that layout. I often start my designs with a critical component. In this case, the component that I was most concerned about was the helix and how it would interface with the layout at Prospect Junction.

Prospect Junction in Denver Colorado - by James Belmont.

Prospect Junction in real life is an important connection. It is a double track diamond of the line into Denver Union Station from the DRGW's North Yard, and provides a connection to the BNSF and UP lines towards Wyoming and Nebraska used by Amtrak. DRGW and BNSF trains headed south for the Joint Line and Pueblo also pass by Prospect Junction. After leaving Denver Union Station, Prospect Junction is the first notable element on the ride west out of Denver.

The critical elements of the junction in my mind are as follows:

• The double diamonds crossing the BNSF main to the Joint Line;
• The bridge over the South Platte River;
• The connection to the BNSF wye for turning and cleaning passenger trains at Denver Union Station;
• Connections to the DRGW line west, the BNSF and the UP lines headed north and east;
• Proximity to the Joint Line traffic headed south; and
• Proximity to the BNSF engine facility.

Unfortunately, the geometry of the junction is not particularly conducive to modeling as can be seen in this aerial view.

Aerial View of Prospect Junction.

My benchwork plan allocated a rectangular area for a helix. The helix supports up to three tracks on 1.5-inch (Ntrak mainline) spacing. This is a greater spacing than I think is necessary, but it provides a little extra spacing in a critical location. The inner loop of the helix does have a 17-inch radius. However, this track is intended for downhill running and I expect that it will be acceptable. Mike Danneman's layout has an 18-inch minimum radius and performs perfectly well. Even at this radius, the grade in the helix is 1.7%. This is only slightly more demanding than the standards used by Ntrak on their Blue Line.

Track Plan for Prospect Junction and the Helix.

I was able to capture the most important elements of the junction, including the double diamonds, the joint line traffic, the ability to turn a passenger train, and the connections at the station. (The bridge over the South Platte River has not yet been added to the drawing.) Trains from the west come into the station using the routing illustrated below.

Routing for Trains arriving from the West (DRGW).

So, trains arriving from the west via the DRGW will actually cross the diamond first on the double track mainline (not prototypical) but then loop around the helix and cross the diamond in the prototypical fashion (one a single track crossing a double track) before entering the station throat. To then reverse the consist, the train would back out of the throat headed towards the BNSF/UP yards (just as in the prototype) but rather than coming around a wye as in the prototype, the train simply runs around the helix and back through the junction and into the throat. Effectively, the loop is a reverse loop which is actually going to be less problematic than a wye for the same operation.

Reversing a Passenger Consist.

Furthermore, trains arriving or departing via the BNSF or UP lines that lead north east out of Denver (via the 31st Street and 38th Street Yards) can also enter and exit the station throat as shown below. These trains head in and out of the staging yards located above via the helix.

Passenger Train Connections to Staging.

The plan for Prospect Junction is not perfect (or perfectly prototypical) but it will function effectively both operationally and in terms of faithfully telling the story of a train leaving the station to travel Thru the Rockies...Not Around Them.

Cameron Turner