Are there any viable compressed air vehicles?

So, I have heard of compressed air vehicles for years. I know they have been used here or there for a very long time in history. I understand they are less efficient than other options, but combined with a trompe, would have very little emissions at all. I found a thread from 11 years ago... and the companies they talked about still seem to be mostly in the planning stages, like they were 11 years ago. Anyone heard of anything actually being manufactured?

I've never heard of one being manufactured. The problem is there are a lot of efficiency losses associated with the pressure volume(PV) work that goes into compressing a gas. The one exception I know of is ammonia refrigeration systems. Ammonia will absorb into water, and then you can compress the water as a liquid and boil the ammonium off with heat to efficiently get a high pressure gas. The problem with ammonia is that it's super unpleasant to smell, and it could suffocate people stuck in a car during an accident. As energy gets more expensive in the future I expect to see more ammonia systems put into service, because the reduction in PV work in compressing a liquid over a gas is substantial. Plus you can burn the ammonia after getting some work out of the decompression stage. I have no idea if that's what Toyota plans to do, but it is possible. https://www.enginelabs.com/engine-tech/engine/corrosion-of-conformity-toyota-takes-aim-at-evs-with-ammonia-engine/

There are lots of good applications for renewables generating compressed air, but transportation options aren't on the list IMO.

For mobile applications, there is a devil's bargain: the more energy you store, the greater the weight of the steel storage tanks.

There are some claims that you can go almost 100 miles on something the size of two scuba tanks. Which sounds awesome, but since I have not seen it actually done, only in theory... then I am skeptical.

Anyone curious about compressed air vehicles who doesn't know much about them would do well to check out Low Tech Magazine's articles on the topic.

A fair intro is a contemporary (well, early '00s) article from the BBC discussing a prototype compressed air vehicle. This next one is a bit more realistic and actionable: a human-powered compressed air system for a workshop.

Considering the demand for electric cars, plus the domination of gas- and diesel-powered engines in the auto market, I don't think there's much of a future for compressed air vehicle research, let alone at-scale manufacture.

PS: I love, love, LOVE Low Tech Magazine and all they've released. I own all their books.