Peaks in supply (or, possibly, demand) causing queues

June 13, 2010, 12:53:48 pm

Sometimes I see a queue of my trucks waiting to be loaded, with one sitting inside the yard with (say) 20% load. That will stay that way for quite some time, then the truck will suddenly be fully loaded and all the following trucks will be loaded quickly as well. What's causing the delay in the loading of the first truck? Have all the workers at the factory gone on their holidays? The destination is full? What?

Re: Peaks in supply (or, possibly, demand) causing queues

Reply #1 – June 13, 2010, 01:30:33 pm

If the destination factory is full, the previous factory does not produce anything until the destination factory has consumed its inputs and has some space. That is the most likely explanation.

Re: Peaks in supply (or, possibly, demand) causing queues

Reply #2 – June 13, 2010, 02:18:16 pm

Yes. To expand Hood's answer: In Simutrans model, there is input and ouptut storage on every factory. If everything goes smoothly, the produced stuff just "moves through". If consumer's input is filled, though, nothing is put to producer's stations and its output storage begins filling. Then, once consumer gets some free space again, the whole storage contents are suddenly dumped into stations in one go.

There are two ways you can fill consumer to its capacity:
a) supply only some of its inputs, so it doesn't process the supplied stuff (you won't do this)
b) supplier produces more than the consumer can handle - badly balanced chain

If this keeps happening in long term, it's a symptom of (b). One bad thing that it does is, it makes you overinvest in transport capacity, since later it becomes unused. You can cure this to some extent by increasing consumption / production rates with electricity. If you do this, though, always start at the end of chain and carefully (slowly?) go "downwards" towards raw material producers - you don't want to speed up the whole chain, only the parts that can't cope.

edit: I Just realized - if the stations themselves are filled beyond capacity, something similar happens. It's important to distinguish these two cases. Stations overflowing with goods can mean either that the situation can progress to reveal an unbalanced chain (bad), or that you can transport more (good!

). But this isn't your case since you say your vehicles keep waiting for loading.

Re: Peaks in supply (or, possibly, demand) causing queues

Reply #3 – June 14, 2010, 09:59:53 am

In my opinion you should reduce the number of trucks waiting to be loaded... That way the consumer would receive less supply from this factory and won't saturate. Hence the cycle would run smoothly instead of bursts.