The San Jose BART extension and making changes to cut costs

[eldomtom2]

The under-constructed BART extension to San Jose, already facing a ballooning budget and heavy delays, is now reconsidering its option to go for a single-bore tunnel and is now conducting a cost analysis of a twin-bore design under pressure from critics.

Will VTA change its tunnel design for the San Jose BART extension after completing a new cost estimate?

The transit agency is reexamining how much the twin-bore tunnel design would cost.

www.mercurynews.com

With BART’s Silicon Valley extension expected to cost upwards of $12 billion, the Santa Clara Valley Transportation Authority is conducting a new cost analysis of a different approach — the controversial twin-bore tunnel design — largely to assuage vocal critics who feel the agency has been moving in the wrong direction on the project for years.

In 2018, VTA decided on the single-bore tunnel design that calls for one massive tunnel deep underground that will deliver passengers through the six-mile, four-station extension from the Berryessa Transit Center in north San Jose, through downtown and up to Santa Clara. The innovative approach would make it one of the nation’s largest subway tunnels.

Since then, critics have questioned whether that was the right and most cost-effective option and have pleaded with the transit agency to revisit the twin-bore design, which would have shallower, side-by-side tunnels. While that approach may be more standard in the transit world, it would require VTA to dig up swaths of the streets, disrupting businesses in downtown San Jose.

After nearly six years, those critics are now making some headway as Tom Maguire, VTA’s chief megaproject officer, told The Mercury News the agency is moving forward on analyzing the cost of the twin-bore design. The agency currently only has an old, very preliminary cost estimate for the twin-bore option that Maguire called a “much less complete design.”

“I think what matters is that we give a real apples-to-apples comparison,” he said. “That spirit of a fair comparison is something that we carried through the five different peer reviews on the tunnel design that got us to this point, and so we want to make sure that we are comparing the twin bore as it actually would have to be constructed in San Jose, not as an abstract concept.”

Santa Clara Councilmember Suds Jain, who sits on VTA’s Board of Directors, was among the first to sound the alarm — especially in light of ballooning costs. Since 2014, the cost of the megaproject has risen from $4.4 billion to more than $12 billion. The timeline also has been pushed back from a 2026 opening to 2037.

Jain said he asked VTA officials to get a new cost estimate on the twin-bore design because “the conditions have changed so dramatically” since the single-bore option was approved.

One of those changes is the width of the tunnel itself. The original single-bore plan was to create a 43-foot-wide tunnel with the train tracks stacked one on top of the other. But those plans were eventually scrapped as the agency opted for a 48-foot-wide tunnel that has side-by-side tracks, eliminating confusion for riders about whether they’re on the right platform.

The change led to the agency last year purchasing an even bigger custom-made tunnel boring machine that’s 54 feet in diameter. It came with a whopping $76 million price tag, and VTA estimates it will be one of the largest machines ever built at roughly five stories high.

Even though the agency has already made the hefty purchase, Jain believes they can still switch gears.

“If you think about it, $76 million is almost a half of percent of the cost of the project,” Jain said. “If you can save 5% by doing dual-bore, isn’t that a win?”

I thought this was interesting to bring up, since recently there's been a lot of scepticism on the forums about the ability of redesigns to cut costs. Do you think a redesign could cut costs in this case?

 

[edwin_m]

Mention of "digging up swaths of the streets" suggests the twin-bore option might be cut and cover, which would make no sense on several levels, since a two-track cut and cover tunnel is inevitably going to be cheaper than two single track cut and cover tunnels. IS this just misleading reporting or is that what is intended?

 

[eldomtom2]

Mention of "digging up swaths of the streets" suggests the twin-bore option might be cut and cover, which would make no sense on several levels, since a two-track cut and cover tunnel is inevitably going to be cheaper than two single track cut and cover tunnels. IS this just misleading reporting or is that what is intended?

As far as I understand it, the twin-bore design would use cut and cover for the stations, while the single-bore option would mine the stations out from underground.

 

[MarkyT]

As far as I understand it, the twin-bore design would use cut and cover for the stations, while the single-bore option would mine the stations out from underground.

Maybe the single large tunnel with vertically stacked tracks could have allowed platforms within the bored tunnel, with compact shaft access, like Barcelona's lengthy line(s) 9/10, partly open already but still under construction.

From https://www.cat-bus.com/2017/10/barcelonas-line-9-inspiring-montreals-pink-line/

Barcelona's Line 9, currently under construction, is a very interesting for many reasons:
It will be the longest metro line in Europe, with 48 km in total
The metro line will be completely automated
The construction is based on the idea of a single 12-metre wide tunnel, large enough to hold 2 tracks (plus platform) on two levels
The stations are nearly completely enclosed inside the envelope of the tunnel
Despite the high complexity of the line, the overall cost is quite reasonable

 

[eldomtom2]

That was the original plan but then they shifted to a wider tunnel with side-by-side tracks. From the article I linked:

One of those changes is the width of the tunnel itself. The original single-bore plan was to create a 43-foot-wide tunnel with the train tracks stacked one on top of the other. But those plans were eventually scrapped as the agency opted for a 48-foot-wide tunnel that has side-by-side tracks, eliminating confusion for riders about whether they’re on the right platform.

 

[MarkyT]

That was the original plan but then they shifted to a wider tunnel with side-by-side tracks. From the article I linked:

The 'eliminating confusion' assertion seems nonsense. Just because passengers may be able to see trains going in the other direction in some side-by-side platform configuration doesn't prevent them ending up on the wrong platform. Good signage and information systems are the best policies to avoid confusion. The slightly larger tunnel seems unlikely to avoid mining out from the initial bored trace at least to an extent for suitably wide station side platforms, which is the big attraction of the stacked arrangement. A feature of Barcelona line 9 is end evacuation, with long ramps folding up into the train nose that give access to a smooth walkway in the '4 foot' (presumably known as the '5 foot' on Bart!). End evacuation may not be compatible with existing trains and the rest of the existing Bart infrastructure which may be why the small increase in tunnel size was required to accommodate continuous narrow raised side platforms for emergency egress. The Catalan line doesn't use the large stacked tunnel everywhere. In places where the tracks run side-to-side, the tunnel is reduced to 9.04m diameter.

 

[HSTEd]

Looks like standard campaigners trying to disrupt the project by any means available.

its extraordinarily unlikely the twin bore solution will be cheaper, it's just another way to delay the project for another few years

The 'eliminating confusion' assertion seems nonsense. Just because passengers may be able to see trains going in the other direction in some side-by-side platform configuration doesn't prevent them ending up on the wrong platform. Good signage and information systems are the best policies to avoid confusion. The slightly larger tunnel seems unlikely to avoid mining out from the initial bored trace at least to an extent for suitably wide station side platforms, which is the big attraction of the stacked arrangement. A feature of Barcelona line 9 is end evacuation, with long ramps folding up into the train nose that give access to a smooth walkway in the '4 foot' (presumably known as the '5 foot' on Bart!). End evacuation may not be compatible with existing trains and the rest of the existing Bart infrastructure which may be why the small increase in tunnel size was required to accommodate continuous narrow raised side platforms for emergency egress. The Catalan line doesn't use the large stacked tunnel everywhere. In places where the tracks run side-to-side, the tunnel is reduced to 9.04m diameter.

The 'side by side' solution proposed here uses central island platforms. Hence the station would direct all passengers to the same platform.
Here is an image explaining the arrangement. This proposed tunnel is very very large, 14.4m inner diameter

It's a design response triggered by the reality that tunnel volume is not a strong cost driver assuming a large enough tunnel boring machine exists.

The availability of ultra large tunnel boring machines (now up to 19m outer diameter) will revolutionise metro and railway construction in the medium to long term.
Bored tunnels with inner diameters approaching 17m are now achievable.

That said, I still think this solution is silly. Think how enormous the stacked platforms could be with the bigger tunnel diameter!

 

[eldomtom2]

its extraordinarily unlikely the twin bore solution will be cheaper, it's just another way to delay the project for another few years

Do you have any particular studies that show this?

 

[MarkyT]

The 'side by side' solution proposed here uses central island platforms. Hence the station would direct all passengers to the same platform.
Here is an image explaining the arrangement. This proposed tunnel is very very large, 14.4m inner diameter.

The island platform for both directions seems no wider than each of those in the stacked arrangement. That could be major safety issue with crowding at the busiest station. London has been gradually removing remaining narrow island platform configurations, on the Northern Line. Glasgow removed many on its subway too. The reasoning about confusion is baffling. Having all the passengers on the same platform doesn't prevent someone getting on the wrong train. You could argue an island makes it easier to make a mistake if you turn the wrong way at the bottom of the stairs.

It's a design response triggered by the reality that tunnel volume is not a strong cost driver assuming a large enough tunnel boring machine exists.

The availability of ultra large tunnel boring machines (now up to 19m outer diameter) will revolutionise metro and railway construction in the medium to long term.
Bored tunnels with inner diameters approaching 17m are now achievable.

That said, I still think this solution is silly. Think how enormous the stacked platforms could be with the bigger tunnel diameter!

Indeed, but they'd probably not need to be that big so the project might save a little by sticking to the smaller design. The narrow island in the big bore is worst of all worlds. Have they any proposals for the enormous void under the tracks. Looks like you could get an additional track down there.

 

[stuu]

The island platform for both directions seems no wider than each of those in the stacked arrangement. That could be major safety issue with crowding at the busiest station. London has been gradually removing remaining narrow island platform configurations, on the Northern Line. Glasgow removed many on its subway too. The reasoning about confusion is baffling. Having all the passengers on the same platform doesn't prevent someone getting on the wrong train. You could argue an island makes it easier to make a mistake if you turn the wrong way at the bottom of the stairs.

Indeed, but they'd probably not need to be that big so the project might save a little by sticking to the smaller design. The narrow island in the big bore is worst of all worlds. Have they any proposals for the enormous void under the tracks. Looks like you could get an additional track down there.

The platforms are going to be 7m wide, which doesn't seem particularly narrow.... that said the whole design seems madness, the tunnel lining must need to be stronger, and the all the extra spoil removal. Then there is the ongoing need to ventilate an enormous unnecessary space. Be interesting to see the actual sums which led to this design

 

[MarkyT]

The platforms are going to be 7m wide, which doesn't seem particularly narrow.... that said the whole design seems madness, the tunnel lining must need to be stronger, and the all the extra spoil removal. Then there is the ongoing need to ventilate an enormous unnecessary space. Be interesting to see the actual sums which led to this design

7m isn't all that wide for a high-capacity urban system for a growing densifying region into the foreseeable future, considering stairways, lifts, etc. taking up space on the platform, especially as the illustration up-thread suggests no platform screen doors are planned. With stacked tracks, each side platform could have been around the same width giving a total of around 14m in the smaller tunnel, with the stairways and lifts outside the main bore. I'd like to see a fuller justification for the side-by-side idea. Does it result in cheaper station access and fit-out than the Barcelona solution? Does it reduce station staffing? The platform confusion argument alone is extremely lame.

 

[edwin_m]

Apart from Barcelona, I can't think of a metro in bored tunnel that has anything other than twin bores each containing one track. However, I think Grand Paris Express has two track side by side in the same bore.

 

[MarkyT]

However, I think Grand Paris Express has two track side by side in the same bore.

That's the default for much of the historic Paris metro too, though not constructed using modern TBMs clearly!

 

[stuu]

7m isn't all that wide for a high-capacity urban system for a growing densifying region into the foreseeable future, considering stairways, lifts, etc. taking up space on the platform, especially as the illustration up-thread suggests no platform screen doors are planned. With stacked tracks, each side platform could have been around the same width giving a total of around 14m in the smaller tunnel, with the stairways and lifts outside the main bore. I'd like to see a fuller justification for the side-by-side idea. Does it result in cheaper station access and fit-out than the Barcelona solution? Does it reduce station staffing? The platform confusion argument alone is extremely lame.

No that's a good point actually, that would be quite narrow. Actually a solution could be be to have two island platforms end-on, with one track screened/walled off on each, with the access in the centre between the platforms. But then that might confuse people.

The stacked idea seems much more sensible if they are going down the single tunnel route though

 

[edwin_m]

That's the default for much of the historic Paris metro too, though not constructed using modern TBMs clearly!

I'm pretty sure that's cut and cover, where a double track in one tunnel is easier and cheaper than two separate tunnels.

No that's a good point actually, that would be quite narrow. Actually a solution could be be to have two island platforms end-on, with one track screened/walled off on each, with the access in the centre between the platforms. But then that might confuse people.

You'd probably need separate emergency exits at the far end of each platform, so three shafts in total. Whether using this arrangement or a traditional island platform, 7m width is probably only enough for two escalators and a lift, and a third escalator would be desirable.

 

[Backroom_boy]

Do you have any particular studies that show this?

Its obviously a bit finger in the air, but It's;

A single bore / single trip by the TBM (which has already been bought)

Vs.

Twin bores / two passes by a TBM (that seems like would have to be bought again to a different size). Plus extra excavation outside the tunnel for the platforms, plus the cost of extra detailed work on a twin bore design.

But the seemingly bonkers idea to redesign the station so passengers can can see trains going in two directions (why? It wouldn't help without directional signage anyway) has baked in some of these extra costs anyway.

Edit: so the idea seems to be passengers only need to be directed to one platform. Which still seems a wasteful use of a few $B, but BART extensions do seem eye wateringly expensive.

 

[Taunton]

You need to understand that the professionals, for design, etc, generally work on a percentage basis of the overall project cost, both for initial budgeting and the fees they charge. An old rule of thumb was 7% for design, but this can vary. Therefore there is a negative incentive for them to come up with efficient, cheaper designs. Their skill is assessing the maximum that the project can afford overall, then designing something that reaches that amount when estimated, of which they get their percentage, regardless.

Once selected, if they think the project can stand $1bn, they will design one to fit that, for which they will get $70m in fees. Their competitor might have designed one that comes in at only $900m, but will then only get $63m in fees. Silly competitor.

That's a very simplistic view of complex negotiations, but broadly that's how it works.

 

[MarkyT]

Edit: so the idea seems to be passengers only need to be directed to one platform. Which still seems a wasteful use of a few $B, but BART extensions do seem eye wateringly expensive.

So they all go to one platform, then still get on the wrong train if signage is confusing! The provision of bigger tunnels to allow total platform surface area to be halved is bizarre.

 

[edwin_m]

You need to understand that the professionals, for design, etc, generally work on a percentage basis of the overall project cost, both for initial budgeting and the fees they charge. An old rule of thumb was 7% for design, but this can vary. Therefore there is a negative incentive for them to come up with efficient, cheaper designs. Their skill is assessing the maximum that the project can afford overall, then designing something that reaches that amount when estimated, of which they get their percentage, regardless.

Once selected, if they think the project can stand $1bn, they will design one to fit that, for which they will get $70m in fees. Their competitor might have designed one that comes in at only $900m, but will then only get $63m in fees. Silly competitor.

That's a very simplistic view of complex negotiations, but broadly that's how it works.

Can you give any examples of projects run on this basis? I've worked on many design projects in the UK and internationally (but not the USA) and I've never seen one reimbursed in this way. There may be "cost plus" contracts where the designer's profit is a percentage of the design fee, but for these there will normally be close monitoring to ensure the designer only does what is necessary and does it efficiently.

 

[HSTEd]

Do you have any particular studies that show this?

Unfortunately the open literature on TBM costing is not as extensive as one might want, but the original tunnel methodology for HS2 suggests cost of tunnels scaling very approximately with diameter, which is proportional to the square root of cross section.

So for the cost of two tunnels you can have one tunnel of quadruple the cross section. Then add the elimination of mined station platforms and cross passages and the savings add up.

Apart from Barcelona, I can't think of a metro in bored tunnel that has anything other than twin bores each containing one track. However, I think Grand Paris Express has two track side by side in the same bore.

It's only comparatively recently that tunnel boring machines large enough to make this practical became available though.

Given how long the life cycle of metro projects often is, it's probably not surprising that it's not common.

Indeed, but they'd probably not need to be that big so the project might save a little by sticking to the smaller design. The narrow island in the big bore is worst of all worlds. Have they any proposals for the enormous void under the tracks. Looks like you could get an additional track down there.

Not that I know of, but in Barcelona one of the tunnels has one track in use whilst the other continues the spoil removal train for the TBM.
It might be possible to arrange things to allow tunnel fit out to commence before the boring operation is complete.