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Comment by mc32 | Hacker News Reader

As far as I understand it, and this may be outdated, cut and cover is way cheaper than boring. And you only bored tunnels if you had no other choice --like Big Bertha in Seattle. BaRT was mostly cut and cover as obviated by going under Market and Mission streets.

Maybe new boring machines are faster and cheaper and break down less than before.

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Yes, cut and cover is cheaper to execute than using a boring machine in most cases and when possible.

But the externalities of cut and cover can be very expensive (blocks streets, and hurts nearby businessen even to the point of going out of business). Those second order effects, even if transient on a long term scale, can cause expensive hold ups. Other externalities are the need to get around existing infrastructure, some of which could have over a century of continuous use.

So for example in NY it is almost impossible (look at the 2nd ave subway, which is mostly pretty shallow) while in LA cut and cover was no problem at all.

I wonder if the price difference between boring and cut and cover is greater than the cost to just...cover business's expenses (rent, loan interest, payroll) for the time it takes to get cut and cover done on that block. Could we just pay them off?

That sounds like it could be cost effective if one only includes the individual businesses and cover their losses, but it can still cause second order effect harm, like customers changing habits and not returning to the original place. Something to think about. Suboptimal infrastructure is also costly, of course...

Honestly I'd be fine with it if the public agencies just used it as a justification for a eminent-domain style "We're going to do this project this way in the interest of the public, we're giving you some cash to cover your immediate costs, and that's that."

The justification for business owners making profits is that it's payment for taking risks. Why then are we trying to shield them from risks while still allowing them to make profits?

Because we want business to take those risks. In the end I benefit from those businesses - not all of them, but some of them.

Businesses should take risks. However government should not add extra risk without careful consideration.

Business owners making profit needs no justification, that's entirely backward. Anywhere there are people, there are goods for sale. The ones who need to justify themselves are the ones who propose to restrict this. It can be done, I consider the restrictions on the nuclear weapons and slave markets eminently justifiable. But in a free society, the default is freedom.

For private sector projects people do get bought off (in a non-corrupt sense of that phrase) but that seems to be unacceptable for public projects for some reason.

I'm talking about the US here -- no idea elsewhere.

I assume the second private was supposed to be public?

Yes, thanks. I was still in the edit window so I fixed it.

I wonder how many different ways people have tried cut and cover over the years. I'm talking here of the horizontal part of the project, not the vertical. It seems like you usually have one, or maybe two, moving work sites, and they go block by block removing the street, and replacing it behind them at some point. Any business near the sites is choked off from foot traffic for a while, even if the site isn't in front of their door yet.

Is it more or less disruptive if you do a checkerboard pattern instead? Instead of n months of construction around your favorite coffee shop, would it be better to have n/2 months of construction now, and n/2 months of construction in July? Maybe that depends on where you are on the street. If, for instance, you start at both ends, then the businesses in the middle of the cut have construction sites boxing them in for almost twice as long as anyone else does. Or maybe that just means more people of means mad at elected officials.

The problem is the street overall is blocked off for the duration. Sure it looks like only one block is stopped, but in reality people who have to travel that block are backed up all the way, and so they will look for alternate routes for the duration.

If you could build the entire thing in 2 weeks (per year) people would be happy with a full road closure - they would all take vacation for those two weeks. This is for the entire city - close all roads to non-emergency traffic for two weeks, fix them all up - everyone not involved in road work or essential services would just go on vacation. You cannot do this of course, but that is what people really want.

I thought about that too. The problem with trains is that they always need to run in the primary direction of traffic. So you can't really build them on cross-streets and avoid disrupting the main thoroughfares. Otherwise you'd often end up with a train to nowhere. The main exception being when traffic is curved, going around some obstruction that the train can cut across.

I recall when South Lake Union got its trolley, one of the things they pointed out was that property values next to a trolley drop, but property values 1 block away go up more. Everyone wants to be a couple blocks from transit, not living above it. So even if you avoided the main road going parallel to it, you're probably tearing up even more desirable real estate and commercial zoning.

What people often forget about modern cut and cover is that it is only disruptive for a short period of the project because they can put a temporary road deck over the cut and do most disruptive work overnight. Its how LA metro built a subway station in the middle of Beverly Hills.

There are several options to make cut and cover less disruptive. Other options are dig in the sidewall supports, then build the cover over the current road surface, finally dig out underneath. It is still tunneling, but it uses most of what makes cut and cover cheaper than a TBM.

> As far as I understand it, and this may be outdated cut and cover is way cheaper than boring.

When you ignore all the side effects, sure (especially if you also ignore the risks of blowing the timeline).

Trenchless tech is spreading fast even in small-ish (street utility scale) construction.

> Maybe new boring machines are faster and cheaper than they used to be.

I'm not sure that's even the case, AFAIK TBMs are still custom-built for the job, highly geology-dependent, and require a ton of babysitting. If you hit an unexpected patch of really different geology things can get really dicey.

> TBMs are still custom-built for the job

This is semi-true. They are built for the job, but the design is standard. What is custom is the exact size of the tunnel, and thus all the supports.

TBMs generally last a lot longer than the job, so a city could save a lot of money if they planed to keep using their TBM, constantly digging tunnels. Start with a north-south line, then use the same TBM to build an east-west line (or southeast/northwest), and so on. However most cities are unable to find the continuous budget to do that and so when they are ready for the next one the old TBM is no longer worth using, and in any case they no longer have trained crew to run it.

> highly geology-dependent,

Soft water logged earth needs different machines from hard rock. There are combination machines, but if you can determine which you need you save a lot of money ordering the geology specific machine. Get this wrong and you end up with a TBM and partial tunnel under the city.

> require a ton of babysitting.

12 people per shift is the number I've heard (NYC uses double which is one of the smaller reasons things cost so much there). The work is mostly routine though. However the TBMs do break once in a while and they everything stops while you repair them.

There's the construction cost, and there's lost income from the people who voted for you. Not all of the money spent on construction is tax dollars.

Think about every time you've been stuck in traffic because there are 3 roads that get you from A to B, and some jackass at city hall thought it would be a good idea to permit road work on 2 of them on the same day.

We are used to highway on-ramps being replaced in days to weeks, but removing an entire street, digging up everything under it, being careful not to nick the utility lines and pipes, then packing dirt back in around them without tearing them, then rebuilding the street on top, that's a lot. Especially for the businesses on that road.

We end up with transportation solutions that are suboptimal because we don't have the political will to tear off the bandaid. This on-ramp is in the wrong place because the old one was in the right place, but was built in a terrible way and had to be removed for safety while still handling daily commutes.

The article discusses this extensively.

Did you read? Article states that cut and cover is still much cheaper technically, but can end up being practically more expensive due to the political/legal ramifications of the surface disruption.

Depends, Gaoxiong did a C&C and they were able to mostly mitigate the second order effects of C&C. Yes, in some sections some traffic was affected more, but apparently it wasn't widely disruptive. It can be done.

It helps when you can complete the project in a few years and not take a decade to build out a single line. So politics does have an impact on feasibility and practicality of C&C.

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