Alternatively, get good at doing rolling releases so you don't take down the entire system and have some sort of canarying process.

I feel like some BARTs moving and some stuck might be a bit of a worse problem.

I think the rolling stock may be stationary right now. Updates relying on stationery.

Train rolling jokes aside, that makes sense... until it doesn't work.

A traffic control system, the thing that makes sure all trains are in known locations, safely spaced, etc.... might be necessarily centralized. There isn't really a "rolling release" you can do for a single system.

Should they have a separate test system for release before "production", sure. Do they? No idea. Is it identical to production? Clearly not. How does the saying go....

> Everybody has a testing environment. Some people are lucky enough enough to have a totally separate environment to run production.

This is not how software works. Although I guess this isn't quite as catchy:

Assume all software is broken at all times. Constantly try to ensure it works and is secure. Sometimes updates break things. Test before production. Ensure test environments are similar to production. You're going to break things.