Alan Jasper describes how he introduced shunting to students in a Year 7 mixed ability class and in a Year 11 ‘Higher Level’ class so that the students in both classes became fruitfully engaged in exploring shunting ‘tactics’.
I decided to give my Year 7 (mixed ability) class the first opportunity to have a go at Shunting. I was concerned as to how long it would take them to get to grips with it but I was surprised at how quickly they picked it up. I think this was partly due to the fact that I asked several pupils to act as wagons in order to demonstrate the shunting process and then allowed the class to solve simple problems—by moving pupils (who were carrying lettered cards). This was later reinforced by moving some magnetic letters about on the white board and using this to develop the notation I wanted them to use.
A simple introductory problem for students to tackle first – possibly as Alan describes in his article – might be, for example:
Shunt the trucks from... ...to...
The challenge is to shunt the trucks from their original order (blue, green, red – or ABC) on the inward line, so that eventually they are on the outward line in a new order (green, blue, red – or BAC).
It could be done in the following way.
Engine comes in on the outward line, and shunts (pulls) blue truck and green truck into siding:
Points are changed, and engine shunts (pushes) blue truck and green truck onto the outward line:
Engine goes back to get red truck:
Engine shunts (pulls) red truck into siding:
Points are changed, and engine shunts (pushes) red truck onto the outward line:
Engine goes off (down the inward line) leaving the three trucks on the outward line in the new order:
Ten engine-movements, five point-changes, one un-coupling of trucks and one coupling of trucks are required to do this simple bit of shunting!
In Starting Points (Banwell, Saunders and Tahta, 1986) we are reminded that:
Discussion may reveal that there are two basic operations – bringing a truck (or pupil) into the siding and taking one out of the siding. These may be coded by two letters or symbols. One class chose ‘I’ and ‘O’ for ‘in’ and ‘out’ and then gradually changed to numerals 1 and 0.
If we adopt this notation, then shunting from order ABC in direction of intended travel to BAC is represented by 110010, as was shown above.
Students could explore the different orders into which it is possible, on this particular track layout with one siding, to shunt three trucks, then four trucks, then five trucks… (They will need to make assumptions about the maximum number of trucks that the siding can hold at any one time).
Railway points photograph by S. Terfloth
They might also try to find conditions that a string of 0s and 1s necessarily satisfies if it represents the shunting of a train of trucks from one order to another.