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Tweedale - The Ebb and Flow of Coal



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.


Cheers, Alan.

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I rather like that.


As I have mentioned before on various threads about freight traffic I think the secret is not to be completely random, but getting the correct balance between an identifiable regular pattern of traffic, with enough variation to keep it interesting.

Remembering my time in the Bristol Area Freight Centre in the late 1970s there were a number of freight customers who received regular traffic in varying tonnages.

Wapping Wharf coal concentration depot might receive 20-25 wagons daily, but during a cold spell 25-35 wagons, and an additional train was sometimes run. Nearby Filton CCD was smaller but similar variations applied, say 15-20 wagons, or more in winter.





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Quite, quite brilliant, Alan. You did lose me around "The inspiration for the scheme . . . " Do you have it on a spreadsheet for me?


Been reading 'Horselunges' again. You made us wait a couple of decades for Tweedale but it was worth the wait. Now don't go away again!



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  • RMweb Gold

Very clever. 


The "etheral" structures at the back are also very interesting, from a design point of view. For me they actually serve as a fully functioning backscene, creating a sense of depth and space, and a subtle transition to the sky. Fully developed backscenes and scenic breaks can be very effective, but they are not in my view the only available solution. Thanks for the inspiration.

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Thanks Rivercider. Your comments got me thinking that seasonal variations might be easily incorporated into the scheme described above, by simply biasing the initial counter positions above or below the centre line at the start of a month - a few rows above during the winter, a few rows below in the summer. Something else to try.


David, thanks for your comments. I wouldn't know where to start getting this to work on a speadsheet! As to the other, it's true I've had some lengthy breaks away from the hobby in the past, but I reckon I'm pretty well glued in place now.


Thanks Mikkel. I was quite pleasantly surprised at the effect that the plain building shapes at the back had on the look. Perhaps something like that is really all it needs. The stylised look doesn't bother me, and they do give an impression of industrial surroundings, but without having to build fully detailed models! 

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I had rather missed most of this so I have made an interesting journey from the original to today.  I am glad that you have relaxed on the minimal scenery a little, to me that great strength of the concept was that of squeezing several scenes into the space needed for one. Most of us modellers have rather less space than we would like to attempt to model something that in real life is rather large. Modelling a single station does produce some brilliant models but loses the sense of an interconnected system going from place to place. Your scenes each capture enough of the atmosphere to identify the type of place and also the interconnection. This needs your brilliant scenic work to create an atmosphere for each scene.

I find it interesting that you also have a strong interest in operation something I share. I do like the computer. Whether done using a spreadsheet or on paper actually makes little difference it is the idea that is key. As someone who at one period designed and produced (with my team) office computer systems I realised the key was understanding the flow of the paperwork.  Typically in a business the  control of work is down to pieces of paper. Whether the random element is by shuffling cards, rolling dice,  generating  a number by computer or counting the number of birds at the bird table matters little in all cases it is how you use the number generated that matters.


Thank you for such an intresting blog.



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Well this is a hugely appealing concept... I may try and sketch out something similar (and inevitably never build it...). I like the mocked up buildings too - add real presence.

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Hi Don, thanks for your input. The minimal scenery was not such a smart idea in hindsight. Unfortunately it was one of the foundations of the layout concept and the main strategy for reducing the build time. In fact I've been seriously thinking of going back to windowed scenes, but it would mean a pretty drastic upheaval, if not completely restarting from scratch. Operating interest is more important to me now than the looks. That wasn't always the case, just something that has grown in recent years.


Thank you mpeffers. Its always nice to plan layouts, even if you know they'll never get built. I sometimes think there ought to be a repository for all the 'brilliant' but unfulfilled layout ideas folk dream up, so even if the originator takes them no furthur, someone else may find an idea there that is worth pursuing. 

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