Friday, April 05, 2019

Murrbahn: Staging Level Doodles

Murrbahn project - Staging level
I wrote about my plans for the Murrbahn layout project last year. All Murrbahn-related posts are linked here.

This morning I had a realization: Would it be possible to remove the two double-slip turnouts where staging is connected to the mainlines to the rest of the layout, if I ran a track around the outside of the helix?

The plan above shows the staging level of my Murrbahn project. The brown double-track represents the main line south of Backnang towards Stuttgart as it descends from the lower level of the layout. The outer track in the three-track helix represents the Kleine Murrbahn from Backnang to Marbach. The inner two tracks of the helix represent trackage north of Gaildorf/West on the upper level towards Schwaebisch-Hall/Hessental and Crailsheim. Since this is a rather long run in the helix it's double-tracked to allow for opposing movements in and out of staging to the north-end of the visible layout.

All the off-layout destinations are represented by a common staging level. I.e. a train from any of the staging tracks (teal, purple, or green) needs to be able to be routed to any of the outbound tracks and vice versa. In my plans so far,  I tried to limit the size of the helix to the Grosskreis II K-track radius of 61.8cm. I connected the staging return loop inside the helix and resorted to using two double-slip turnouts as part of the arrangement to get trains in and out of staging. This is not bad per-se, but I was not happy about this. Double-slips are mechanically complicated and more prone for derailments. This critical junction is located against the wall, in a tunnel, halfway behind some helix tracks. Not a great place for handling a derailment.

My solution runs the staging access track around the helix track instead of inside. At the cost of 10cm wider helix footprint I gain multiple benefits:
  • No more hidden double-slip turnouts
  • Traversal of at most one thrown turnout pair to get from staging to either portal track and vice versa
  • More gentle curves for staging access, in particular no sharp S-curves
Since I can start the ramp a bit earlier than with the old plan, the helix tracks raise high enough that the yellow track can duck under the helix for about 30  centimeters to avoid additional intrusion into the aisle at that tight spot. 

The first turn of the helix extends into an oval to allow inclusion of a regular turnout to branch the inside track of the helix for simultaneous up and down movements on these 15-20 meters of track. I expect to need about 5-6 turns to climb from staging to the upper level. On the second turn the helix tracks move as far into the corner as possible to minimize intrusion on the lower level.

Nevertheless, that leaves a minimum 3 ft of open space -- more at staging level and below -- enough to put an operator position inside the helix. This position will control traffic in and out of staging, and act as station operator ("Fahrdienstleiter") for Waiblingen, Hessental, and Marbach. This position will probably need a couple cameras to watch what's happening in the staging yards.

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