The author keeps asserting the "inherent weakness" of steel-on-steel railways; however, there are very good reasons it has been settled on as a good choice. Friction and sound losses are generally minimized, thanks to a very small contact surface and smooth, hard materials with little give; wheels can be re-machined back into spec a couple times rather than being replaced; rails can be re-used for lower-speed applications when worn; unlike pneumatic tires, steel can be machine into conical, self-centering, turn-adapting geometries with fixed axles and no need for differentials; the list continues and is quite long. Apparently, a recent change to wheel geometry reduced wear and extended lifetime by as much as 40%.

See Practical Engineering's latest video: https://www.youtube.com/watch?v=Nteyw40i9So

There was also a design with a layer of rubber between an inner steel wheel and a thin outer steel tire.

That was used by high speed trains in Germany - until one of the steel tires broke at 300 kilometers per hour and got stuck in a switch, causing the train to detail and hit the support column of an overpass, which collapsed on top of the train. 101 people dead: https://en.wikipedia.org/wiki/Eschede_train_disaster

> a comparable carriage fitted with pneumatic tyres could need as many as 20 wheels.

How does a bus get by with far fewer wheels?

I think the answer is that they are still building with the same weight as a train, rather than a bus.

That points out an unexplored engineering envelope for modern trains, made possible by newer technologies:

* Very light trains. Think lighter than road cars, since they don't need crumple zones or crash worthiness.

* Virtual coupling. Basically platooning on rails. Now the cars need to at most push/tow one other disabled car, so they don't need a beefy chassis to support towing long trains, coupling forces, etc.

* Homogenous cars. They all have traction motors, small batteries and sensors and compute. Think a low-range Tesla on rails.

* Autonomous control. Self-driving on rails. No operator cab. Since the train is now quite light, with a reasonable stopping distance, obstructions on the track can be potentially avoided so long as the sensors are adequate.

* Much faster acceleration and deceleration. With leaning, they could also corner faster.

* Probably intrinsically quieter, but now pneumatic tires would probably have reasonable life.

> Not just inefficient

What? I thought wheel deformation was a huge source of drag and steel tires were one of the main reasons why trains were comparatively efficient.

Still in use on a few lines of the Paris Métro

Can somebody explain to me the difference between this „short lived experience“ and the actual ongoing decades long operations of tire based metro/subway systems?

https://en.m.wikipedia.org/wiki/Rubber-tyred_metro

The fun experiment was the paper wheels.

https://en.wikipedia.org/wiki/Paper_car_wheel

I remember this thread from hn. Tire dust makes up the majority of ocean microplastics - https://news.ycombinator.com/item?id=37726539

Link to the article - https://www.thedrive.com/news/tire-dust-makes-up-the-majorit...

Japan has a train-on-tires on an elevated overpass track around Tokyo bay.

It's pretty neat.

> Very light trains. Think lighter than road cars, since they don't need crumple zones or crash worthiness.

Crashes involving light rail are common in urban areas, because the trains share streets with cars. I don't see that going away as long as human-driven cars are allowed. And because passengers are often standing, the trains must be heavy to improve passenger safety in crash situations.

> Virtual coupling. Basically platooning on rails.

Modern designs typically have very long cars, with only 1, 2, or rarely 3 cars in a train. Longer cars increase passenger capacity and improve space utilization, because passengers can move around freely. They also allow busy passengers save some time by exiting from the right end of the train.

> Much faster acceleration and deceleration. With leaning, they could also corner faster.

Urban trains already limit acceleration and deceleration to improve passenger safety and comfort. Long-distance trains with sitting passengers and grade separation are another matter.

> I think the answer is that they are still building with the same weight as a train, rather than a bus.

A non-trivial part of this difference is that train cars are generally bigger than a bus. Light rail is generally more bus sized and they are generally closer in weight (though still heavier).

> * Homogenous cars. They all have traction motors

Electric passenger rail systems generally already use EMUs which have a power unit per-car or per pair of cars.

> small batteries

I'm not sure how you're going to have a small battery in a bus-sized vehicle that needs to operate fairly continuously for a good portion of the day unless this is on a partially electrified ROW. EMUs with smaller batteries to serve such routes already exist FWIW.

I think there's a reasonable case to be made to adjust US passenger rail regulations to allow lighter cars (especially in the context of high-speed rail), but allowing pneumatic tires seems like a poor motivation for it.

  A non-trivial part of this difference is that train cars are generally bigger
  than a bus. Light rail is generally more bus sized and they are generally
  closer in weight (though still heavier).

That's been tried.

It did no go well, and was hated by both crews and the public. Rode extremely rough because it turns out it's a very different optimization needed.

https://en.wikipedia.org/wiki/Pacer_(British_Rail)#Analysis

Train crash worthiness is quite an interesting topic. Important to remember is that trains carry hundreds of people. So a crash involving a single train carriage can easily become a catastrophe.

https://www.youtube.com/watch?v=ewr-4TvG810

That's essentially a light rail system. Have a look at the Montreal REM.

Excellent ideas. In the US, metropolitan rail transit systems need a dramatic reimagining. They are expensive, slow, and often crime ridden. Would love to see their right of way put to better use.

The reason why metros on tires is a thing is that they used to have much better acceleration/breaking characteristics than rails, which is good for metros since you can cram more trains in the same lines this way.

I said “used to” because, from what I understood, the development of ABS made breaking characteristics of traditional trains much better than before, which reduces the improvement you get with tires.

(Don't quote me on that though, I got this from a coffee machine discussion with a former metro driver when I was working for RATP 10 years ago so my memory may not be 100% accurate at this point)