Hamilton, New Zealand
A small dockside shunting yard branches off a busy commuter line. The up and down mainline tracks emerge from and enter tunnels at right. Commuter trains run up and down all day (modelled by one two-car DMU shuttling between fiddle yards continuously).
Late at night the commuter trains are infrequent, and a locomotive delivers full 20-foot hopper cars to the dockside (front) siding from the down mainline. Empty hoppers are removed from the rear siding to the up mainline. During the day, hafnium ore is loaded onto barges and empties must be shunted ready for pickup from the cramped yard.
Both the Trackmobile’s compact size and its ability to jump sidings using its road wheels are required for operations. Operation consists of moving cars from full-side to empty-side staying clear of mainline traffic. A diagram shows the allowable occupancies, clearing mainline traffic. The trackmobile is equal to a single hopper car.
At the end of the yard the sidings protrude one carlength into a short tunnel. The operator can “jump” the trackmobile between unoccupied end positions, representing operation on tires. (The operator’s hand is concealed from view by the short tunnel.)
How to accept 7 full hoppers to an unoccupied yard and shunt empties for return next night? Darn, the solution does not fit inside my 250 words… yours to solve. Many other puzzles are possible. Can you find one that cannot be solved without couplers on both ends of the Trackmobile?
(NOTE: This layout may not require any alterations to the Trackmobile, which can be used directly from the box.)