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Comment by tcbawo | Hacker News Reader

Here is their project page: https://www.boringcompany.com/chicago/

Why does this need to have battery? The skates will be mechanically confined to a concrete track as they describe, wouldn't it be easier to power them as high speed rails are powered?

This is almost certainly a project to prove parts of their technology, which is part of Musk's greater ambition, and not an "optimal" solution to this particular problem. I think his end-goal here is to create a series of tunnels with skates for cars which his electric cars can drive up to, and then be ferried to their end destination at high speed without traffic.

They've said they want to power their TBM via batteries instead of running miles of high voltage cable. A similar rationale would probably apply for powering the skates.

Don't you need a really long extension cable to charge the batteries?

That's essentially what conventional TBMs use - high voltage extension cables to power electric VFD-driven motors. If you use batteries, you can drive them out of the tunnel and recharge anywhere.

Which also means that passenger loading and unloading can happen outside, thus substantially reducing station costs too.

I feel like this this project will eventually morph into an undersized subway.

Which seems like a reasonable concept - if the big cost of subways is wide-diameter tunnels, experimenting with narrow subways is worthwhile. A Subway with a limousine form-factor, for example. But it's absurd how many permutations will have to happen before we land there.

If you have the kind of nice geotechnical conditions that permit the use of tunnel boring machines then tunneling isn't actually very expensive. What's killer is the cost of subway stations, which need to be dug out manually.

Unless the stations are put on the surface.

I thought cost-savings from a system that used narrower bores was the key to Musk's whole strategy? I thought that was the whole thing - by designing smaller hardware he could make underground transport affordable?

To clarify, I was talking about traditional subway construction and why changes in boring costs would not change that.

> if the big cost of subways is wide-diameter tunnels, experimenting with narrow subways is worthwhile.

It's not. The tunnels generally account for at best 1/3 the cost of a subway project, and even then, the cost of the tunnel that's variable per diameter is an even smaller fraction (since you're sticking a lot of other stuff in the tunnels). The big money sinks tend to be the underground stations. Overall, moving to a smaller diameter tunnel might save you around 10%, and you'd probably eat up much of those savings with rolling stock incompatibility issues.

Maintenance might be simpler with modified Model X's than an electrified rail with contacts.

Especially since the Blue Line is parallel so they could probably share substations.

A battery would seem to increase the stakes in case of an accident.

With either a fixed power rail next to the track or overhead lines, if there's an accident the power can be removed, and all that can burn is the vehicle.

It is scary to think about one of these batteries burning inside the tunnel...

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