[jcranmer]

Not necessarily. The key cost savings that Musk envisions boils down to "build tunnels that are too small to put existing rolling stock in," which means that if the proposed personal rapid transit system turns out to be like every other PRT system and not work well, you're left with a tunnel that is too small to be useful for anything else.

[bluGill]

Well this tunnel is only a couple miles long. Put in some lights and humans can walk the whole length to get around. It seems like a moving sidewalk could be put into this tunnel.

[komali2]

This would be pretty nice to have in hot as fuck Vegas.

[ncallaway]

> The key cost savings that Musk envisions boils down to "build tunnels that are too small to put existing rolling stock in,"

Do you have a reference for that? My understanding was that over the long term the goal was to develop cost savings through better boring machines themselves, not through just by reducing the cross-sectional area of the tunnel.

I thought they were starting with smaller cross-sectional areas and working their way up as they developed machines, but by understanding of the end-goal of The Boring Company was to be able to build large tunnels at 1/10th the cost of current processes.

[jcranmer]

All of the innovations that are cited on The Boring Company's FAQ are things that are already done (e.g., reusing TBMs, or continually operating TBMs), or related to the "new" transit system and the virtues of narrower tunnels (which are overstated--at the size of tunnels we're talking about, cost tends to scale linearly with diameter, not cross-sectional area).

[Retric]

Making an existing tunnel wider is vastly cheaper than building an equivalent tunnel from scratch. Simply knowing the soil composition makes a huge difference.

In hard rock you can use drilling and blasting across long sections rather than just the leading edge. Alternatively, a TBM needs to remove significantly less material.

[the-dude]

Are you sure about that? Because I have never heard about a tunnel project which has been 'upgraded' this way ever.

And if I start to think about the practical problems, like breaking up part of the tunnel before widening it, it quickly seems like building a new one might be more efficient.

[Retric]

Assuming the tunnel is not in use then yes.

Here the are filling the tunnel and using a TBM. https://www.newcivilengineer.com/farnworth-tunnel-widening/1...

Widening an existing tunnel without interrupting traffic is still possible like: https://www.rocksoil.com/pdf/233_r.pdf. Though with increased costs.

However, this changes for under sea tunnels which are segments placed down and thus can’t really be widened.

[NeedMoreTea]

Almost every tunnel has a lining that makes widening prohibitive. Which is why the London Underground is forever stuck with small tunnels on the original lines.

[Retric]

A larger issue is the underground is in use forcing you to do something like: www.rocksoil.com/pdf/233_r.pdf

That and the cost vs benefit is not considered worth it.

[jcranmer]

But more expensive than building the tunnel the right size to begin with, when you take into account the cost to build the too-small tunnel in the first place.

[the-dude]

It is common courtesy to indicate you have editted your post.