Elon Musk just gave the media a tour of his 1.5 mile prototype tunnel under Los Angeles, which he spent US$10m to build. Why are Elon Musk’s tunnels so cheap? Because they’re tiny.

As media photos of the event will show you, the tunnel is just slightly wider than a car. That means that if you used it for a train, it might have room for one seat per row. I suppose you could fit two if there was no way to move through the train while it was between stations, but that’s almost unimaginable once you add a required emergency exit plan.

So despite Musk’s occasional noises about using his tunnels for public transit, this thing is for moving cars, which means it is for moving trivially tiny numbers of people.

As we’ve discussed before, a car-based tunnel also requires elevators. You zip your car into a parking space and it descends to the tunnel. Cool, but have they run the numbers on how many of these they would need, assuming it takes, say, a minute to do a full cycle of the elevator? How much real estate would it require to get cars into the subway at a rate that even maximizes the tiny capacity of the subway?

Anyway, those are some questions to ask today.

And yes, it would be great if this dalliance produces genuine improvements in tunnel technologies useful for building actual train-sized tunnels that can move the number of people who need to move. But Musk’s prairie-dog burrows are mostly hype, confusion, and elite projection. While delivering almost nothing useful, they are confusing elite opinion about whether we still need to build mass transit, which we do. Is any marginal benefit worth the resulting delay in getting the infrastructure we really need?

Two lessons to remember:

If it doesn’t scale, it doesn’t matter. The media are easily excited by demonstration projects, but this idea doesn’t scale. You could build lots of tunnels, and they would each move so few people that they wouldn’t make a dent in a city’s transport needs.

If it doesn’t scale, it’s for the rich. Or to put it another way: Inefficiency is inequality. Anything that spends a lot of money to serve small numbers of people raises the question “why are those people so important, and what about everyone else?”

Does this remind you of other transport fantasies, such as replacing transit with “service to your door”? These rules about scalability are pretty good tests to bring to all the fun new inventions, including whatever’s coming next.