I'm not one for doing much modelling in the cold dark days of winter, and progress on the layout is only just starting to resume after fizzling out way back in the autumn. However the trains have been running regularly during the interval, and over the past few months the layout has become a testbed for trying out a new operating scheme, which has seen the line running as a single-commodity railway for the transport of coal. I'll start by saying that it is far from being a wholly realistic simulation of coal movement, but I find it interesting to operate, and that is really all I ask of it.
The sketch above shows how the coal railway operations have been overlaid on the existing track plan by simply designating convenient locations for the purpose, regardless of what is actually on the ground.
The inspiration for this scheme actually came from a 1960's-era card game called Stocks & Shares. The game basically involves buying and selling shares using Monopoly-style money, the winner being the one who makes most profit. The point of relevance here is that it has a rather neat randomisation system for fluctuating the share prices, which I thought I might be able to adapt as a way of varying the supply and demand for goods on Tweedale. For testing the idea I decided to just apply it to coal traffic.
Shown above is the cardboard computer that controls the traffic movements. No doubt the digitally-minded would be able to do all this on an Excel spreadsheet or something.
At the heart of the adaptation is a 'Load Indicator Card' on which counters indicate the current daily traffic (in wagon loads) for each industry. There are 19 rows and the number of columns depends on the number of industries. The first 4 columns here are for the customer demands (steel works, gas works, power station and coal merchant). The 5th column shows the daily output from the coal mine. The final column records the coal stockpile at the mine. The loads in the customer columns range from zero at the bottom to a maximum value equal to that industry's siding capacity at the top. The output values for the mine range from 0 to 8 (for no particular reason).
A shuffled pack of cards controls the movement of the counters up and down the columns. There are 6 cards for each industry, with values of +4,+3,+2,-2,-3,-4. For the mine and 4 customers that equates to 30 cards. The idea is that as a card is picked from the pack, the appropriate counter is moved up or down by the number of rows indicated.
Tweedale Railway's No.7 (ex Mainline J72) swaps empties for fulls at the mine's exchange sidings. Due to the low capacity of the sidings, several trips may be needed during the day. Basic scenery was added to this section in the autumn, along with a grey sky background and lighting from a single strip of LEDs. While this would probably give insufficient illumination for representing a bright sunny blue-sky day, it seems to work well enough with the dull overcast here.
One of the things I like about this system is the way that it evolves. The traffic flows vary over time in an almost cyclic manner, rather than being completely unpredictable from one day to the next as in some of the more unruly randomisation systems around. After a while emerging trends can be detected, which allow planning ahead to a certain extent, such as the strategic placement of wagons for the following day.
To initialise the game (I can't help but think of it as a game), the counters are placed in the middle row of the indicator, and the cards are given a good shuffle. I should add that the layout is run most days for about a half hour stint, and this fits in nicely with a day's worth of coal movements. Picking, say, one card per day from the pack to update the indicator, gives about a month's worth of play before reshuffling the cards. However the evolution of the traffic flows can sometimes be rather slow. As can be seen from the indicator photo above, moving a counter doesn't necessarily mean the number of loads will change. If I'm feeling impatient at having the same wagon movements for several days in a row, I may pick more than one card to help speed things up.
This siding at Slaghill Junction is standing in as the gas works for now. Low relief shapes have been dropped down the back, pending more detailed structures later. To make them less obtrusive they were painted with the same grey emulsion as the sky background. I found this resulted in a very peculiar visual effect that makes them hard to focus on, but I kind of like it - sort of ethereal, if that's the word, as if the buildings are looming out of the smog.
One other thing that needs to be dealt with is when the supply and demand drift too far out of balance, which they may do once or twice during a cycle of the pack. There are a couple of rules covering such eventualities, and this is where the coal wharf comes in.
Rule 1 - If demand exceeds supply and the mine's stockpile drops to zero, coal supply is switched to imported coal from the coal wharf, until the stockpile at the mine has recovered to 8 wagon loads.
Rule 2 - If supply exceeds demand and the mine's stockpile increases to more than 15 wagon loads, then excess coal is exported via the coal wharf, at 3 wagons per day, until the stockpile has dropped to the 8 wagon loads threshold.
On the other side of the dividing backscene, the track is in place but little else. The coal merchant, wharf and power station are merely represented by temporary placeholders. The line in the foreground, currently in use as an industrial siding, will eventually form the main line to the coast. Health & Safety inspectors are gently steered away from this area of Tweedale!
At the beginning of the day the indicator is updated by the clerk at the mine. The mine's output value is added to the stockpile column. After the clerk has calculated the number of empties required, he sends his order to the yardmaster. It's then time to take on the role of train crew and get busy, moving empty and full wagons between the yard, the mine and the customers' premises. As wagons are loaded at the mine (removeable loads), the stockpile value is reduced accordingly.
I'm still tinkering with the system, but I like the way its going. While it may not get applied to general goods in the greater scheme of things as the layout expands, I can see it being useful for controlling a slowly evolving background movement of bulk traffic such as coal.