Author: Barry Cott

There is a concept in the software development world called the “minimum viable product“. From its Wikipedia entry, a Minimum Viable Product (MVP) is “one with just enough features to satisfy early customers, and to provide feedback for future product development.”^[1][2]

I thought I would extend the concept to model railroad layout design to determine what would be the simplest design that met my goals for the MQR. A Minimum Viable Design is largely concerned about how trackage is connected to each other; concepts like the the geometry and length of the mainline, the minimum radius of curves, easements, siding length, etc will not be finalized until the final layout design.

For my former garden railway (pictured above), I could argue that the minimum viable design was in fact a circle of track. At that time, I really wanted no more than a loop of track to run my one train. The layout had two switches on it but I hardly used them at all.

Givens for the MQR

• The design must support continuous as well as point-to-point operation, representing both ends of the line (Coed-y-Parc and Port Penrhyn)
• Steaming-up of engines must be done off of the mainline track.
• For the point-to-point option, it must be possible to prepare the train for its return trip without having to physically pick up any rolling stock or locomotives. This requires a runaround track at every end of the line. Turning of locomotives either by a turntable or wye is not required; the prototype Penrhyn Quarry Railway did not turn their locomotives.

Minimum Viable Design for Single Train Operation

It was reviewing Rob Bennett’s Weston Railway design that gave me the idea of the Minimum Viable Design concept: I liked the way Rob put the two “ends” of his railway beside and parallel to each other (lower right corner) but was concerned about the number of switches it took to implement.

Things clicked when I doodled out a design where the runaround trackage was shared by both ends of the line. To make this work, I felt it would be necessary to create some sort of visual separation between the two ends of the line.  The prototype Penrhyn Quarry Railway helped out here with the long slate wall on the south side of Coed-y-Parc.  Such a wall would not look out of place in Port Penrhyn either. This insight led to the MQR MVD #1a:

This design requires just 5 switches to meet the givens listed above for single train operation; the trade-offs are that: 1) for the runaround move, a locomotive must make use of the track at the other end of the line; 2) physically the two ends of the line must lie together and some means of scenically separating them must be devised. On the advantage side, this arrangement creates a working wye so that locomotive direction could be reversed if desired.

Typical operation would go like this:

1. A train can be steamed up on either side but let’s assume the train is built up and steamed up on track B.
2. It proceeds on track C towards the mainline.
3. Entering the mainline on track D, it can extend its run using track E.
4. To complete its run, the train enters track F and stops on track G. The locomotive is uncoupled from the rolling stock.
5. The locomotive moves to track A, then backs up through tracks B and H until it reaches track F.
6. The locomotive then pulls forward and recouples to the rolling stock on track G, ready to return.

Adding one switch removes the need for sharing the runaround trackage between the two ends and allows Coed-y-Parc and Port Penrhyn to be physically separated. This represents the MQR MVD #1b design:

This fundamentally is Rob Bennett’s Weston Railway design stripped back to its basics. Typical operation would go like this:

1. The train is built up and steamed up on track B.
2. It proceeds on track C towards the mainline.
3. Entering the mainline on track D, it can extend its run using track E.
4. To complete its run, the train enters track F and stops on track G. The locomotive is uncoupled from the rolling stock.
5. The locomotive moves to track I, then backs up through track J until it reaches track F.
6. The locomotive then pulls forward and recouples to the rolling stock on track G, ready to return.

Here I think the addition of one switch would substantially improve the overall operation of the layout, despite losing the wye.  In addition, it will make it much easier to scenic as Coed-y-Parc and Port Penrhyn no longer need to be co-located. In the next post, I will review the design in the context of operating two trains.