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So we know how an industry decides to allocate the cargo that it has supplied, however, we have yet to determine how the amount of cargo an industry produces per month might change. Each month the game randomly changes the amount of production of some industries, and this can be done one of two ways depending on the rules in use – either the default/TTD-like economy rules or the smooth economy rules. We will be looking at the smooth economy rules which can be set under the advanced options menu like shown below.

OpenTTD: Smooth economy

Smooth economy rules

The chance for a production change each month is 4.5%, i.e. 4.5% of producing industries from industry list change production, and this is combined with one of three conditions.

  • Poor or no service, i.e. less than 60% of cargo transported: 33% chance of increase, 67% chance of decrease in production
  • Good service, i.e. more than 60% of cargo transported: 67% chance of increase increase, 33% chance of decrease in production
  • Excellent service, i.e. more than 80% of cargo transported: 83%% chance of increase increase, 17% chance of decrease in production

These two, the chance for a production change each month and the chance of a decrease or increase based upon service level, are multiplied together, i.e. 4.5% × 33% = 1.5%, resulting in the following.

  • Poor service: 1.5% to increase and 3.0% to decrease
  • Good service: 3.0% to increase and 1.5% to decrease
  • Excellent service: 3.75% to increase and 0.75% to decrease

With the smooth economy option enabled, production changes per month are between 3 and 23%. Industries with very low production, i.e. 12-40 tonnes per month, will have higher changes.

Primary industries produce cargo eight or nine times a month, although forests can produce cargo up to ten times per month. Monthly production is an industries ‘base value’ × the number of times a month cargo is produced. For example, the base value for a coal mine is 15 tons, so the monthly production is 120 or 135 tons. This base value is capped at 255, so the maximum possible monthly production for any industry is 2040 or 2295 (or 2550 – again – forest).

This table lists possible starting productions governed by the smooth economy patch. Like previously mentioned, production is a multiple of eight or nine, and sometimes ten with forests.

Raw Material Industry Produced Cargo Initial production range
Coal Mine Coal 56 to 176
Forest Wood 48 to 152
Oil Rig Oil 56 to 176
Farm Grain and Livestock 40 to 112
Copper Mine Copper Ore 56 to 112
Oil Well Oil 48 to 152
Iron Mine Iron Ore 40 to 112
Bank Valuables 24 to 64
Gold Mine Gold 24 to 80
Diamond Mine Diamonds 24 to 80
Fruit Plantation Fruit 40 to 112
Rubber Plantation Rubber 40 to 112
Water Supply Water 48 to 152
Farm Maize 40 to 128
Lumber Mill Wood 180 or 225 (if trees available)
Cotton Candy Forest Cotton Candy 48 to 152
Battery Farm Batteries 40 to 128
Cola Wells Cola 48 to 136
Plastic Fountain Plastic 56 to 160
Bubble Generator Bubbles 48 to 152
Toffee Quarry Toffee 40 to 112
Sugar Mine Sugar 40 to 128

Well, that’s great and all, but it doesn’t make it any easier to visualise. So for example, say that a coal mine has 70% of its output transported, meaning that it has good service. Because of this, there is a 3% chance, because 4.5% × 67% = 3%, of a production increase from 3-23%, and a 1.5% chance, because 4.5% × 33% = 1.5%, of a production decrease from 3-23%. Let’s see how much the industry might grow after the first year. To do that, we need to take these percentages and, instead of worrying about the 3-23%, we’ll take an average of 13% for the amount of production change.

(1 + (0.03 – 0.015) × 0.13) ^12 – 1 = 0.0237

So the coal mine in question will grow an average of 2.37% after the first year. How about another example? Let’s say that the industry has a rating of more than 80%, meaning that there is a 3.75% chance of an increase and 0.75% chance of a decrease in production.

(1 + (.0375 – 0.0075) × .13) ^12 – 1 = 0.0478

In this case, the industry will grow approximately 4.78% after first year. After looking at this, it is pretty evident that it will take a while for an industry to double its production – for good service, it would take 29.6 years on average to double, and with excellent service, it would take 14.8 years on average to double. Assuming that, in game time, a day is 2.36 seconds, the doubling time with good service would take 7.1 real hours, and the doubling time with excellent service, would take 3.6 real hours.

However, in game, industries will seem to be changing their production rate very randomly when compared to what we have just covered. This is because the above examples are only true when observing many industries over the long-term, since individual industries may greatly deviate from these averages used. Statistically speaking, six out of ten industries will not go from 100 production/month to 2100 production/month even with the best service during a 65 year period, and about one out of nine industries will even lower their production when being served at 60-80% cargo transported for a 50 year period.