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Elon Musk is boring a tunnel to skirt gridlock

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Re: Elon Musk is boring a tunnel to skirt gridlock

#151

Post by ziedaniel1 »

Robotbeat wrote: post #118
DonnyV wrote: post #81

I talked a little about this last week. I think he wants the tech to bore a hole close to the core of Mars and set off a nuke. This would restart natural lava flow in Mars which would then create self sustaining magnetic field. https://news.ycombinator.com/item?id=13598876

That is not possible. At some point, your tunnel starts collapsing under the pressure and the great heat makes tunneling incredibly difficult. The deepest we've ever gotten on Earth is the Kola Superdeep Borehole (a Soviet project) that got 12km deep. On Mars, with the lower gravity and cooler center, we may get about triple that before reaching similar constraints in pressure and temperature. But no way you can get…

Wow, can I read more about the circum-planetary superconductor idea somewhere? I thought this sort of thing wouldn't work because superconductors lose superconductivity once currents get too high, as you mention.

Re: Elon Musk is boring a tunnel to skirt gridlock

#152

Post by WorldMaker »

owenversteeg wrote: post #119

Ok, so one thing I've noticed reading the 120 comments in this thread and the article is that literally nobody knows anything about boring, or tunnels. Musk knows nothing, he put someone in charge who knows nothing, the reporter knows nothing, and the commenters here even admit they are completely guessing and know nothing about boring/tunnels. I definitely don't know anything about tunnels. It's a joke that came to…

« Is there enough boreable space under our cities that this is doable? I know Musk says he wants to go deep, but even at very deep depths you run into problems of sand, boulders, geography, etc, etc. »

Certainly out here in a much more karst [1] part of the country (I'm in Kentucky specifically) there's just about no way, from what I read, to bore under our cities without threatening the geologic stability of just about everything above it, because our cities are already essentially built "on top" of caves, caverns, and limestone hollows. Sinkholes are a real problem with sometimes deadly effects.

Tunnels in general here can be very expensive to cover survey costs and insurance. I am not a civil engineer, but I would assume there are probably maintenance tasks and costs that differ for this sort of geology.

[1] https://en.wikipedia.org/wiki/Karst

Re: Elon Musk is boring a tunnel to skirt gridlock

#153

Post by monodeldiablo »

Inconel wrote: post #87
monodeldiablo wrote: post #79

Earlier quoted context omitted.

I've never had any issues with Amtrak's service. People forget that they're second-class citizens to freight on the track, so they're usually not to blame for being late and they're held back by the infrastructure, which is designed, owned, and maintained by freight companies. I know it's accepted in the HN community to be down on government monopolies, but a quick glance at the privatization disaster of British Rail…

I'm not at all discounting your point, but isn't Japan's rail system made up of various private rail companies? Or are those quasi governmental?

I believe it's half-and-half. I think they fully privatized the JR regions that earn decent profits, but the government subsidizes/operates the less profitable regions. I honestly don't know much about it, though.

Re: Elon Musk is boring a tunnel to skirt gridlock

#154

Post by jartelt »

mrfusion wrote: post #123
dahart wrote: post #68

We can't afford to maintain the surface roads & bridges we already built, and tunnels are more expensive and require more maintenance by like an order of magnitude. (I made that up, but I'm pretty sure it's right, to within an order of magnitude... but if tunnels are 1000x more expensive, then I'm wrong). I can admire someone who has the resources to exclude himself from the traffic problem instead taking action to t…

I wonder if maintenance would be cheaper. Think about it. A constant temperature. No rain or sun. No freeze thaw cycle. No salt. Those are all things that damage roads.

Perhaps, but in a tunnel you have to deal with preventing water leaks and pumping out ground water, maintaining ventilation systems, lighting, etc. Plus fixing things like potholes will be more costly in a tunnel.

Re: Elon Musk is boring a tunnel to skirt gridlock

#155

Post by cossatot »

owenversteeg wrote: post #119

Ok, so one thing I've noticed reading the 120 comments in this thread and the article is that literally nobody knows anything about boring, or tunnels. Musk knows nothing, he put someone in charge who knows nothing, the reporter knows nothing, and the commenters here even admit they are completely guessing and know nothing about boring/tunnels. I definitely don't know anything about tunnels. It's a joke that came to…

There are two main problems with increasing depth: Rocks and water.

Rocks are the biggest. The ratio of rock to finer sediment increases with depth until bedrock is reached. This might be anywhere from 1 to 1000 meters depth but in most cities it's probably Bedrock can be bored through and is quite strong, but it's slow and may be more expensive (although it could cut down on regulatory and post-boring structural reinforcement costs quite a bit).

Mixed soft sediment and large boulders are often trickier to deal with--the boring rate can vary wildly, and it's difficult ta maintain the proper rate balance between cutting and sediment removal. Remove too slow and things clog, remove too fast and the pressure becomes too low and voids can develop, which are then filled in by overlying sediment as the ground above collapses a bit.

Shallow seismic techniques could certainly be used for imaging/boulder detection some number of meters in front of the borer if it was built in right. But I don't know how useful it would be. Can they steer or reroute? Probably not much...

Water is a lesser concern but is still important. The water table is pretty shallow (<10 m almost everywhere) and tunnels need to be sealed. This is pretty straightforward, but I really wonder about LA during an earthquake with a deep transit tunnel (especially in winter when the water table is higher). What if a long tunnel's walls are seriously breached? Could it flood and drown passengers who may be blocked by debris etc?

Re: Elon Musk is boring a tunnel to skirt gridlock

#156

Post by skybrian »

tgb wrote: post #40
elbigbad wrote: post #34

Earlier quoted context omitted.

Do you happen to have any examples of where induced demand has not happened? My understanding is that it is pretty much guaranteed, especially in larger cities. I think New York's bridges and tunnels are the canonical examples of this. I say pretty much because I assume there must be cases where it didn't happen, but I am unaware of them.

Maybe induced demand has always happened, in the sense of demand increasing when the product is more available. But it's plenty common for the amount that demand increases to be less than the amount of extra capacity available. Furthermore, is induced demand that bad? If you double the capacity and it again gets filled to the point of gridlock, well then at least twice as many people are now able to be in gridlock, w…

It's possible to change the incentives.

If the roads are free they fill up until gridlock makes them more painful than the alternatives. If you charge money then the expense becomes part of the cost/benefit calculation. It favors car pooling, rich people (who don't care about the price) and other people who urgently need to get somewhere during rush hour (who can pay the price that one time).

You can also just do car pool lanes, which has some similar benefits.

Re: Elon Musk is boring a tunnel to skirt gridlock

#157

Post by ska »

IpV8 wrote: post #115
jandrese wrote: post #90

Earlier quoted context omitted.

One thing that isn't as obvious at first is how tunneling traffic under a city can greatly increase the walkability of the city. Look at Boston after the Big Dig. Neighborhoods that were previously cut in half are coming back together. Downtown is seen as a desirable place to be. It's a big QoL improvement for a city. I'm not sure if he will be able to bring the costs of tunnel boring down as much as you would like,…

Not sure if the Big Dig is a great project to reference here, it went over budget by some 200% and many years. It was seen as one of the greatest civil engineering mistakes by the end. Sure it improved the QoL, but what other projects that take less than some 15 billion dollars can improve QoL just as much?

There are lots of lessons to learn from the Big Dig - but I don't think one of them is that the eventual cost and time overruns were strictly necessary. Also: regardless of the implementation issues I think it is interesting to look at how it has affected Boston after completion. If only to identify any positive effects and see if you can work out how to achieve similar ones at lower cost.

Re: Elon Musk is boring a tunnel to skirt gridlock

#158

Post by dahart »

noja wrote: post #82
dahart wrote: post #68

We can't afford to maintain the surface roads & bridges we already built, and tunnels are more expensive and require more maintenance by like an order of magnitude. (I made that up, but I'm pretty sure it's right, to within an order of magnitude... but if tunnels are 1000x more expensive, then I'm wrong). I can admire someone who has the resources to exclude himself from the traffic problem instead taking action to t…

Isn't the problem with traffic (in most places) that people are using the roads at the same time?

Yeah, totally. At least that's one way to look at it. There are multiple right answers. Lowering driving rates helps, flexible work hours helps, increasing public transportation helps. Any of these would diffuse traffic jams, and no there's no one single problem and no one single solution -- unless nobody drove at all.

But that's why building tunnels doesn't seem like the best first-line defense. It's expensive, and it's fixed and inflexible, and doesn't reduce demand. It could help, but it could also hurt unless tunnels are less expensive to build & maintain than roads.

I was trying to be playfully sarcastic by saying the problem with traffic is traffic. Most larger cities in the US, there's only a traffic congestion problem during rush hour, accidents, and road construction. (The city I live in does enough road construction every year, enough that it's widely considered to be a top contributing factor to traffic congestion.)

LA traffic, which is what the article referred to, is worse than that, it's density is getting high enough that traffic congestion lasts all day in some places, rush hour is not just slow but crushing, and accidents can and do routinely prevent tens of thousands of people from working. It does seem like there must be a large economic cost to LA's traffic.

Re: Elon Musk is boring a tunnel to skirt gridlock

#159

Post by jcranmer »

JoeAltmaier wrote: post #100
AlexandrB wrote: post #96

Earlier quoted context omitted.

Actually you should think in 4D. In the future all those tunnels require maintenance that is much more complex and expensive than maintenance for surface roads. If the US is not able to keep its roads in good condition (and in many places it's not), how is building more expensive roads underground going to solve the problem long term?

Roads need maintenance almost exclusively because of the weather - sun and rain, heat and cold. Underground, none of those things. We have tunnels today that are a century old with only minimal maintenance, right?

We have tunnels that are a century old which are in danger of complete failure. Underground structures tends to exacerbate issues with water intrusion and drainage, not to mention persistent problems with air quality (air can only diffuse effectively in 1 dimension, not 3).

Re: Elon Musk is boring a tunnel to skirt gridlock

#160

Post by paulddraper »

adamjc wrote: post #2

I thought the current thinking was that building more roads means that there will be more roads to use, and therefore more cars on the road. https://en.wikipedia.org/wiki/Induced_demand

In economics terms, demand is a relationship between price and quantity demanded.

Increasing the supply doesn't affect demand; it just changes the realized price and quantity to another place in the same demand relationship.

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