Proper interlocking would have prevented the clearing of the main signals when the crossover was open; a block system would have given the signalman the means of ascertaining the approach of trains, and the means of refusing the approach if his station was blocked by shunting operations.
32.
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.
33.
The power source code is'D'for diesel,'A'for AC traction,'C'for DC traction and'CA'for dual tracti only operation,'P'for passenger trains-only operation,'M'for mixed operation ( both passenger and freight ) and'S'for shunting operation.
34.
We left our rear truck in the siding here . . . [ At Siddlesham ] we performed some marvellous shunting operations, which occupied six minutes, and which resulted in our entering on the last stage of our journey, with three trucks in front of the engine and two behind our carriage the very best example of a " mixed " train it has ever been my fortune to behold ! . . . Just before reaching Selsey we passed through the only cutting and under the only road-bridge the line possesses, pausing a few minutes to get rid of our five trucks at a siding.
35.
The line was signalled and worked on the train staff and ticket system, and the Anstruther to Boarhills section, previously operated as one engine in steam, was to be converted also to the train staff and ticket system . ( Hutchinson recommended that the Leuchars to St Andrews section should also be converted to this system . ) Gradients on this section were steep, the most extreme being 1 in 49.5, and Hutchinson was concerned about steep gradients at siding connections, where there was a risk of vehicles being left on the main line on the gradient during shunting operations, and by some mishap running away.
