Train shunting puzzle

Shunting puzzles usually consist of a specific track layout, a set of initial conditions (typically the starting place of each item of rolling stock), a defined goal (the finishing place of each rolling stock item), and rules which must be obeyed while performing the shunting operations.

There are often constraints such as making the minimum number of couplings and uncouplings, or making the minimum number of junction direction changes, or completing the puzzle within a specified time limit.

Other important factors may include the lengths of tracks limiting the number of rolling stock vehicles which can be placed along them.

Some train shunting puzzles have been developed as add-ons for railway simulator computer programs such as Auran's Trainz and Microsoft Train Simulator.

Shunting puzzles tend to fall into the following categories, but this list is not intended to be exhaustive: Two of the best known model railway train shunting puzzles are: