Tunnels!

[talindsay]

Back in 2003 I asked a Met Council person why they hadn't considered elevating the (Hiawatha) line through downtown to remove grade conflict and the dude laughed dismissively, saying it would interfere with the skyways. That seemed like an unsatisfactory response to me, but Metro Council has clearly never taken elevated lines in the downtown seriously. And to be fair, they *are* ugly and disruptive, and the skyway problem is real.

I've also heard that our tunneling costs are relatively low compared to most places, and so the cost difference between elevating and tunneling is smaller than in most places. Basically if it's not worth tunneling here, it's not worth elevating either given the small difference in cost and the substantially higher disruption and environmental impact of elevated rail.

[DanPatchToget]

While Miami doesn't have skyways (that I know of) their Metro Rail is elevated above their People Mover system in downtown, so that's probably the closest example of what elevated rail in Downtown Minneapolis would look like. I don't think anyone is proposing building the tracks through the skyways and then we have to deal with many grade crossings in skyways, but rather have the tracks go above the skyways.

[Tcmetro]

I think the downtown at-grade alignment is fine. Considering there's no long-term plan to add a third line to the 5th St corridor there isn't much need. I'd even be surprised if 7.5 min peak frequencies come back before the next decade.

As for the cheap tunneling, I believe it was first considered in the late 60s. The idea is that limestone is relatively easy to dig through. The problem is that the limestone layer is like 80 feet below ground, so stations would be quite expensive to build. The initial subway plan had stop spacing of 1-3 miles.

[DanPatchToget]

I think the downtown at-grade alignment is fine. Considering there's no long-term plan to add a third line to the 5th St corridor there isn't much need. I'd even be surprised if 7.5 min peak frequencies come back before the next decade.

As for the cheap tunneling, I believe it was first considered in the late 60s. The idea is that limestone is relatively easy to dig through. The problem is that the limestone layer is like 80 feet below ground, so stations would be quite expensive to build. The initial subway plan had stop spacing of 1-3 miles.

From a near term perspective yes the 5th Street Corridor does the job. Long term however, I don't think it's in our best interest to rely on a corridor that's already at capacity.

[Nick]

Man, does anybody remember the argument on here like six or seven years ago about whether or not train frequencies would increase on 5th Street with the Blue and Green Line extensions?

[Anondson]

All the time.

[Tom H.]

Vividly.

[Anondson]

So what is the geological extent of this pressed sand layer which was mined by the Ford plant?

I understand the greatest costs to subterranean transportation are to stations, but if this layer is this stupendously easy to excavate how far does it stretch underground?

https://www.startribune.com/did-ford-mo ... 600006618/

[luigipaladio]

The Twin Cities are underlain by layers of sandstone and limestone. You can get an idea of the geology by taking a look at the cliffs on either side of the Mississippi gorge in St. Paul and to some extent in the gorge between Minneapolis and St. Paul. The University has a couple of buildings that were tunneled at least ten stories below the surface for the advantages of a stable year round temperature and security among other potentials.

The limestone is loaded with spectacular fossils in many areas - not of dinosaurs, but of sea creatures dating back to a period when this region was a sea bottom.

There are problems in some areas, such as parts of Downtown Minneapolis, where underground streams have eroded considerable voids in the layers of stone, but by and large, both the limestone and the sandstone are relatively stable - as long as they are not exposed to weather conditions or high volumes of water (think about the rapid erosion of St. Antony falls when the flour millers built numerous tunnels to funnel water to their mills).

As a kid - this dates me - I toured the sand mines under the Ford plant. This was before the word "Liability" was a big factor in daily life. The "sand" was stone until it was ground up. As rock goes, sandstone is relatively easy to mine. With the high water table and numerous underground springs and streams, I suspect any effort to do an extensive system of deep tunnels would have more than a few challenges - not unsolvable, but expensive.

[Anondson]

Maybe tunneling under downtown would be a bad idea.

https://www.theguardian.com/environment ... hington-dc

[DanPatchToget]

Keep in mind New York's subway system is very old, so of course ventilation systems probably won't be as advanced there as modern subways. I wonder if their subway trains used to have brake shoes made with asbestos back when that material was common. If that's the case then at least that stuff isn't in the air anymore.

I remember when I was in Oslo in 2018 they had a few small plants growing on the platforms for the regional trains serving the underground Nationaltheatret (National Theatre) Station to make the air cleaner. I don't know if that's still going on and if it's worked, but a modern subway can still have modern ventilation.

[alexschief]

Yeah, this is a problem to be solved, not a fatal conceptual flaw.

Air filters, better ventilation, different brake technology, etc.

[StandishGuy]

Other U.S. cities like Houston, Austin and Portland are in the midst of planning for construction of subway tunnels for their LRT lines through their downtowns to improve speed and capacity. Has the Met Council, Hennepin County or Minneapolis ever seriously studied the idea of constructing a tunnel for buses or LRT this century? IMO the Nicollet corridor from around 38th St through downtown should be studied for a subway considering the existing and growing density, cluster of jobs and high existing transit ridership. The cities above have far lower population density and their downtowns pale in comparison to Minneapolis during non-COVID19 times. It seems odd that there doesn't appear to be any momentum to even study the concept considering Minneapolis' recent growth, the 2040 Plan for increased density and a Transportation Action Plan goal of getting people out of their cars.

Seattle is also constructing a subway through their International district in preparation for a new LRT line to the eat. There's even an advocacy group called Seattle Subway that is pushing to construct a subway out to the Ballard neighborhood sooner rather than later.

Even small cities in Europe such as Copenhagen, have subways while the best we are able to hope for is ABRT sometime in the 2030's or 2040's through the densest part of our region. Obviously, the cost is very high for a subway, but the ridership would be potentially very high- especially if it were expanded across the river and due to connections to other high frequency transit. Is Minneapolis just too low-density for this to make sense- even in 20 years or more?

[VacantLuxuries]

I think it's more the 'ribbon cutting problem.'

Everyone wants to go to a ribbon cutting for a new, shiny piece of infrastructure. The powers that be fund these projects so they can stand with the big scissors and be a part of the celebration.

Nobody holds ribbon cuttings for routine maintenance. These projects get kicked down the road and overlooked in favor of more new things that can be publicly celebrated.

A subway tunnel to improve travel times on existing transit is more routine maintenance than it is a shiny new object to celebrate. It doesn't add miles to our system, it doesn't involve contracts for new trains, it's hard to show a picture of to the voters who will complain about what their tax dollars are being spent on. And so it's not considered, even though it would have numerous benefits to our transit system and should have been part of the initial Hiawatha line to begin with.

[Silophant]

We'll see, but I've suspected that downtown being the end of the line makes the slowdowns seem like less of a problem than they would if they were happening in the middle of the route. I'm hopeful that there will be some more movement towards fixing the downtown problem once SWLRT is up and running and people are getting on in Minnetonka, zooming for six miles through portions with full priority, then stopping for a stoplight every 300' for a while on their way to the U.

[Trademark]

I think it's more the 'ribbon cutting problem.'

Everyone wants to go to a ribbon cutting for a new, shiny piece of infrastructure. The powers that be fund these projects so they can stand with the big scissors and be a part of the celebration.

Nobody holds ribbon cuttings for routine maintenance. These projects get kicked down the road and overlooked in favor of more new things that can be publicly celebrated.

A subway tunnel to improve travel times on existing transit is more routine maintenance than it is a shiny new object to celebrate. It doesn't add miles to our system, it doesn't involve contracts for new trains, it's hard to show a picture of to the voters who will complain about what their tax dollars are being spent on. And so it's not considered, even though it would have numerous benefits to our transit system and should have been part of the initial Hiawatha line to begin with.

A new tunnel is definintly ribbon cutting material. And it will receive much more media attention then any aBRT line ever would

[Trademark]

Other U.S. cities like Houston, Austin and Portland are in the midst of planning for construction of subway tunnels for their LRT lines through their downtowns to improve speed and capacity. Has the Met Council, Hennepin County or Minneapolis ever seriously studied the idea of constructing a tunnel for buses or LRT this century? IMO the Nicollet corridor from around 38th St through downtown should be studied for a subway considering the existing and growing density, cluster of jobs and high existing transit ridership. The cities above have far lower population density and their downtowns pale in comparison to Minneapolis during non-COVID19 times. It seems odd that there doesn't appear to be any momentum to even study the concept considering Minneapolis' recent growth, the 2040 Plan for increased density and a Transportation Action Plan goal of getting people out of their cars.

Seattle is also constructing a subway through their International district in preparation for a new LRT line to the eat. There's even an advocacy group called Seattle Subway that is pushing to construct a subway out to the Ballard neighborhood sooner rather than later.

Even small cities in Europe such as Copenhagen, have subways while the best we are able to hope for is ABRT sometime in the 2030's or 2040's through the densest part of our region. Obviously, the cost is very high for a subway, but the ridership would be potentially very high- especially if it were expanded across the river and due to connections to other high frequency transit. Is Minneapolis just too low-density for this to make sense- even in 20 years or more?

Nothing will happen to change transit in this city unless groups form for advocacy of a real network based approach for our cities transit. Especially as we get out of covid and people start moving again we need to propose a plan and advocate one on one with transit riders so they contact their representatives to make this happen.

[alexschief]

Other U.S. cities like Houston, Austin and Portland...

You missed Dallas, which is further along than any of them. The D2 subway project (a light rail tunnel through downtown that will relieve but not replace the existing at-grade trunk) was approved locally yesterday.

I think Joey has it correct. A prerequisite for the kind of political pressure and financial support that will support a downtown tunnel is service on both ends of downtown. Currently the delays in downtown Minneapolis are mainly a problem for Metro Transit's operations folks, but they do not impact riders a great deal. But once the system through-runs downtown, with destinations on either end, those delays will become a lot less tolerable. Not just because they will impact riders who experience them, but because they will have wider impacts on frequency throughout the system.

I wouldn't be surprised if, by 2025 or so, there starts to be formal talk about this. Something to watch would be the extent to which congress and USDOT fund the FTA's Core Capacity grants program, which is where the federal contribution would come from. Currently, core capacity grants go to projects that:

- Are located in a corridor that is at or over capacity or will be in five years
- Will increase capacity by 10% (or greater)
- "Not include project elements designated to maintain a state of good repair"

I think downtown Minneapolis LRT trunk would meet these requirements.

[Silophant]

I think it already does. My understanding is that a train every 2.5 minutes (so, 10 minute frequency on two lines) is the absolute max they can get through the downtown stoplights, hence the Blue Line frequency dropping slightly when the Green Line opened in 2014. So I guess it depends on how you define "at capacity" - all the seats being full on a given number of trains per day? All the seats being full and some number of people standing?

[StandishGuy]

No

I clearly remember that an elevated line was seriously considered through downtown for the Hiawatha Blue Line. True that skyways were a concern, but many people including the downtown business community had experience with the "L" loop in downtown Chicago that is noisy and creates an unattractive streetscape. The cost was likely a lot higher too considering the need for elevators, removal of skyways, etc.