Post #1746129

2025-11-30 02:01 UTC

I didn&#39;t realize that Swiss trains apparently also adhere to the &quot;schedule for 80% of capacity rule&quot;. Apparently trains in Switzerland go around 80% of the top speed possible on the track. The 20% overhead is used to make up time in the case of delays. The thinking is: stable and predictable operation is more important than going faster. Because the cost of passengers regularly missing layovers is much higher than the benefits of trains being 20% faster.

Replies (3)

@yosh@toot.yosh.is 2025-11-30 02:05

Slack, overhead, and spare capacity are not inefficiencies to be ground down, but integral to the stable functioning of systems. Because a system without buffers cannot absorb shocks.

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@esoterra@hachyderm.io 2025-11-30 02:06

@yosh@toot.yosh.is plus, you often get higher efficiency or lower wear and tear running equipment with more margin

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@skade@hachyderm.io 2025-11-30 07:00

@yosh@toot.yosh.is Uh, uhm. I took a PhD course on how to model this and arrive roughly at that number (long story on how I was allowed to do this, even though I only hold a Masters). We did this on server-client systems, but what is a train but a request traveling through the internet. Essentially, you can take timed petri-nets (a form of state machine with multiple states being active at once - think "trains on routes, in stations") and use a statistical function to model how long it takes for an token (train) in that net to go to the next state (every edge has a different function, runlength). You can then actually reason _locally_ about states at every node using markov chains. ("how many trains are at this station at any time with which probability") and then _back_-calculate that into delay probabilities. Biggest learning: this isn't linear. It's almost linear, until the point it breaks, where delays grow rapidly and catastrophically over the network. Which is also why 70% system load is about the moment where you should start thinking about upgrading your servers. Sorry for the brain dump :).

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