Wayne Roderick, 3rd Division, PNR, NMRA (life)

10/09/98 rev 01/16/07

The Teton Short Line is a North-South bridging railroad in the Rocky Mountains of Idaho and Wyoming that connects the East-West Great Northern and the Union Pacific transcontinentals. We handle interchange traffic as well as serving our own customers, so holding yards at the ends of the TSL were needed to receive and originate the interchange trains. We struggled with this problem for several years using "under the layout" holding tracks that proved to be extremely unsatisfactory because you can't see and service them readily. Finally, after extensive negotiations with the appropriate real estate manager we acquired a narrow right-of-way on two walls of the adjoining utility/recreation room that was dominated with a pool table. The trackage had to be under removable glass or plastic covers to avoid cue sticks.

staging.jpg The upper staging yard at ThunderMountain with one of the clear plastic covers removed. The lower yard is partially seen in the shadow below. Short lengths of PVC pipe identify the train AND prohibit it from accidentally moving out. The PVC jams between the turnout guard rails and the engine frame without risk to the coupler or derailment.

If you've looked at the track plan, you may have noticed the "tail" hanging down on the left side. That's CUE BALL siding, the Offline (OFL) yards and Thunder Mountain (TM) that make up the OFL holding and staging system.

By using a wye integrated with a single turn helix, we mangaged to make the OFL upper and lower yards exist at BOTH ends of our mainline. Eastbound traffic enters OFL upper yard via CUE BALL and Westbound traffic enters the OFL upper yard via the one way connecting track from the West end of Malfunction Junction (MFJ).


It can get to be a bit confusing, especially because the cyan colored tracks are under the lift-out foam mountains, so we provide our new crew people with this 3.5" x 5" pocket picture to help clarify it all.

All interchange and through trains, East or West bound, terminate at one of the OFL yards and can later originate as a "new" train from either the West or the East. The two yards can hold eleven trains while leaving a runner track open in each. The two Offline (OFL) yards are stacked with seven inches separation, which may seem tight, leaving only 3-1/2 inches of head room to reach into, but it's only 12 inches deep and accessible along it's full length. The bottom yard has been constructed so it can be easily slid out for corrective maintenance if needed. Only the very accessible front three tracks in the lower yard are used for tearing down and building new trains. The remaining tracks are for holding trains.

Thunder Mountain (TDM) needs some explanation. The real estate manager insisted that we provide downstairs toilet facilities for our Thursday night crew, so we scouted around and found an appropriate facility. :-) T.Mtn Loop Click on the thumbnail for a picture. The Thunder Mountain loop encloses that facility and includes a 42" lift bridge for easy access. Because the loop around Thunder Mountain is a tight (24 inch radius) and descending curve, we usually bring trains into the upper yard and run downhill only.

For simple show purposes, or to keep some action when the operation degenerates to coffee, railroad tales and lies, trains can run via the West belt loop or traverse the extended loop via Thunder Mountain.

Stage1 pix Incoming traffic enters the upper five track yard from CUEball siding or MFJ. Outbound traffic exits the lower yard via the double crossover. The crossover feeds any of the eight tracks into the West end or the East end of the railroad. This creates an "interesting" polarity problem that will be addressed further down the page.

Stage2 pix

Under the staging yard is drawers to hold more cars. We can keep up the variety of cars and trains on the layout this way. The drawers hold some unit coal, PFE reefer and passenger and excursion trains that only run once in a while.

Stage3 pix To the left of the operator you can see the five upper tracks converging to enter the decending Thunder Mountain loop. Below is the incoming end of the loop. Overhead is the Ross's Rolling Rock mine, the exclusive source of Mithril ore, at the extreme high end of the Termite TImber Line.

Stage4 pix Departing the upper 5 track yard a dwarf ground signal warns of an open drawbridge OR a track polarity error (you know, the old reverse loop thing). An engineer must approach a RED signal at a walking speed and STOP if it does not turn GREEN to indicate an automatic polarity correction. It should remain RED only if the TDM drawbridge is not locked down. Power is removed from the track if the bridge is not safe.

Stage4 pix This is the view from the bottom yard where we expect to see incoming traffic from the TDM loop. The GREEN dwarf signal works the same as above. Overhead you see the Tortoise switch machines for the upper yard. These are embedded horizontally in the 3/4" substrate for overhead clearance and use simple music wire linkages to the turnouts.

AutoReverse.pix I am often asked about using off-shelf, short sensing devices (automatic reversers) to switch polarity in the staging yard. I'm an electrical engineer and the idea of routinely permitting a fault is contrary to my way of thinking, so I don't do shorts! I see it as a brute force, brainless solution for the electrically timid folks. Others have studied and documented wheel pitting from using these gadgets.

Each yard, upper and lower is connected via a great big wye so it can be reached from either end of the railroad. I use conventional 50+ year old techniques to align the yard with the turnouts. The computer switches a polarity relay based on turnout positions but the technique is basic. Where it gets a little sticky is in the Thunder Mountain Loop that connects the two yards, each of which might be either polarity. The simple solution is to connect the loop only to the appropriate yard. In the two previous photos you saw a white overhead lamp that illuminates a photocell buried between the ties. The hardware (not computer) connects the loop to one yard or the other when the photocell is obstructed. The connection remains until another photocell detection changes it. The cirucuit also senses an open bridge situation. An open bridge kills the track power, shorts out the rails to stop a multi-unit lashup, and sets both dwarf signals RED.

TMI, "Too Much Information" my grandkids say. The TSL engineering department has never been accused of keeping things simple, so if you are interested Click for the details including control with the Parallax Stamp. Schematics and code too. Actually, this is the way we used to do it before converting the railroad to CMRI which greatly simplifies everything

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