GPS doesn’t work underground though.

But the problem described in the article seems rather unique to NYC and one has to ask how other subway systems manage just fine without artificial slowdowns.

I'm pretty sure the person you're replying to was saying that the original speedometer mechanism in their 1955 car is accurate to within 2-3 km/h of the speed reported by GPS, and thus suggesting that this pre-GPS mechanism ought suffice for the subway / be better than whatever they currently use.

You can simulate the GPS if you wanted to, drop cables down to pipe through the real signal, or simply do very basic positioning with custom radios underground.

OP is correct. We have significantly better techniques.

For what it's worth, a metro train does around 100,000 miles per year.

And every single one of them invariably is when i'm not onboard.

So do most normal trains, and they all have speed gauges that work fine, rain snow or dust. Clearly the technology exists.

NYCT was, until this year, operating R32 trainsets still limping along from the 1960s that were repeatedly life-extended as newer (1970s) train types experienced structural failures & delivery of their planned replacement trains was repeatedly delayed. It's obviously possible to maintain old trains, but generally expensive & challenging, especially when they're still doing 100,000 miles a year, and things clearly slipped.

Especially because the trains were operating well past their planned lifespan because their replacements were ordered but not delivered, so the major overhaul that would that would normally be done to life-extend a train kept running for decades didn't happen.

That's fair. And also, the environment is probably different, as in more dust in the tunnels, etc.

But to stick with French technology, the Paris metro, for all its issues, does have working speed gauges. Some lines still use rolling stock from the 60s and 70s.

So, considerably less than the average articulated lorry, or indeed Skoda Octavia?

* * *

You must live somewhere without a lot of road haulage, or without any taxis.

I don't have the link to hand. It was figures from a forum for drivers discussing what "average mileage" would mean on a British articulated lorry.

Go fix it then :p