Owner David Townend and track designer Steve Davies sat down and started devising alternative solutions. On about the 39th iteration, they hit on the idea of a huge under-layout storage helix on a 35-metre loop rising on a grade of about 1 in 100. The concept was to have three complete loops under the layout, each with storage capacity for 60 trains giving a total of 180 storage tracks of varying lengths. This would be enough to hold the entire McKinley fleet covering that 20 year operating cycle.

The design consists of four main areas:

• 1 - There is a single oval track which descends in a helix at a 1 in 50 grade from the operational track down to the bottom storage level.
• 2 - There are three identical vertically-stacked storage levels.
• 3/4 - There are three large train yards on each level; two are through-track and one is a dead-end storage area suitable for DMUs and HSTs (which are designed to run forwards and backwards without the need for turning).

The design is relatively crowded allowing just 230mm of vertical separation between decks. This requires the storage boards to be very thin, yet rigid enough not to sag between supports. We used 9mm birch plywood as the base with 40mm edge boards keyed onto the sides to provide rigidity. The risers are 6mm steel rodding which have a very narrow footprint. We identified that we would have to pre-assemble the wiring and electronics on the underside of these storage levels. That necessitated designing the boards into manageable sectional pieces that would be fitted together after wiring and testing was completed.

Above the three storage levels, the fourth level (Level D) will be the main operational layer on the layout extension. The two connections to the existing layout and entry and exit from the storage system will be made at this level. Half of Level D will be visible and will house the Sheffield area of track. The hidden part will contain the connections as describe above.

Finally, Level E sits above the hidden area of Level D and will be the final layer of trackwork. The two operating areas of Wakefield and Halifax will sit on this uppermost level.

Steve Davies laid out all the storage areas in Auto-CAD which is more commonly used in the manufacturing and construction industries.