Downtown Minneapolis LRT Tunnel Discussion

[Silophant]

I've gotta imagine that, without cross streets and parking garage entrances, a Marquette tunnel would be able to handle all the Nicollet Mall local buses and Marq2 expresses (however many that ends up being in the flexible-work/suburban LRT world). Nicollet might be even better, but, y'know, rather not rebuild that again until the 2050s or so.

[Korh]

I'm assuming no one is in support of an elevated option through downtown for at least a few reasons.

[DanPatchToget]

Well on one hand the skyways would require an elevated alignment to be built above them, which increases cost, but on the other hand the skyways could be modified to allow access to elevated stations and make it easier for light rail riders to access downtown buildings.

[StandishGuy]

IMO the Minneapolis Transportation Action Plan (TAP) that was approved in 2021 should have included at least a mention of either/ both the possibility of constructing a downtown LRT and bus tunnel I submitted feedback to that effect, but Public Works folks did not address the ideas in the 10-year plan. In fact the transit section of the TAP is pretty underwhelming with few details and a modest vision for the City and downtown specifically. There's a few mentions of bus lanes and studying new bus routes in the plan.

[nBode]

I'm sorry if this has been covered before, but can someone explain how these issues can't just be fixed with 100% signal priority at intersections?

[daveybabymsp]

I'm sorry if this has been covered before, but can someone explain how these issues can't just be fixed with 100% signal priority at intersections?

You could probably fix the light rail issues that way, but it could potentially create issues for buses and cars that have to cross the light rail tracks. With blue line and green line trains headed in both directions potentially every ten minutes or ideally frequently, that could cause significant issues


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[BoredAgain]

I've gotta imagine that, without cross streets and parking garage entrances, a Marquette tunnel would be able to handle all the Nicollet Mall local buses and Marq2 expresses (however many that ends up being in the flexible-work/suburban LRT world). Nicollet might be even better, but, y'know, rather not rebuild that again until the 2050s or so.

I like your optimism in believing that a bus tunnel will happen before the 2050s. I recommend starting the lobby now for putting a tunnel beneath Nicollet when it gets revitalized again. Actually moving the buses (and taxis and maybe even the streetcar) off of our pedestrian mall will make the pedestrian experience so much better that any other improvements they through into the mix will just be icing on that cake.

Room for access portals will be easy if the street above remains car free, though it should still be designed for food truck and farmer's market access. I would put the south end between Alice Rainville and 12th. The north end portal location would probably be between 3rd and Washington, but if you can extend the tunnel north and exit between second and 1st parallel to Hennepin, I think that would be neat, but it would limit bus access to the tunnel.

[MinneapBliss]

There are a couple journal articles from 30 or so years ago that address issues with tunneling (for track and for stations) in the area. You can download one titled "Underground Station Design Issues for Light Rail Transit in the Twin Cities Geology" by John Carmody and Dr. Raymond L. Sterling.

Here is a link to the other: https://www.sciencedirect.com/science/a ... 6293901409

For the sake of efficiency, heat, and access control points, I wish the conditions were otherwise, but the Met Council might need to get creative to achieve those things within our LRT system. Obviously there is a completed tunnel section at the airport, so it's not that it can't be done; it's just that other geologic conditions are much more favorable for this type of underground infrastructure.

[nBode]

I'm sorry if this has been covered before, but can someone explain how these issues can't just be fixed with 100% signal priority at intersections?

You could probably fix the light rail issues that way, but it could potentially create issues for buses and cars that have to cross the light rail tracks. With blue line and green line trains headed in both directions potentially every ten minutes or ideally frequently, that could cause significant issues


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Yes but what is a normal light cycle? 2-3 minutes? How long does it take a train to clear the intersection? 1-2 minutes? I don't see how this can't be easily coordinated. The LRT should absolutely have priority over both buses and cars—it's higher capacity. Even if it causes issues (which "significant"? How? In what scenario? ?) at some certain times, it would still be worth it.

I was assuming this has been scientifically studied by the Met Council or someone, no?..

[Anondson]

I’m sure it will be helpful to be able to explain why the storm water can be tunneled, like is currently being reconstructed, but a train carrying tunnel takes different geologic concerns.

[MNdible]

Lots of people talk about how the Minneapolis geology is ideal for tunneling, but that's only true if you're looking at a very deep tunnel that cuts through the sandstone beneath the Platteville limestone cap. This isn't really feasible for an LRT tunnel that would require long, expensive elevators and escalators to access deep stations (not to mention ventilation, emergency egress stairs, etc.). Obviously none of these things impact a stormwater tunnel.

A shallow tunnel (and that's the only thing that would be feasible for serving downtown) would need to sit atop the limestone cap, which means you're talking about a cut-and-cover tunnel through the glacial till. That also means you're limited to the clearance between existing building foundations, and while in general there should be room to fit everything you need there, it will be pretty tight. These hypothetical underground stations will be wider than the aboveground stations that they're replacing, because the vertical circulation will chew up space -- think the size of the Lake Street or Terminal 1 stations.

[StandishGuy]

I couldn't seem to read the second journal article for some reason.

The first one entitled "Underground Station Design Issues for Light Rail Transit in the Twin Cities Geography" was pretty interesting. It was written in 1992 and describes challenges with constructing LRT tunnels in three places- downtown Minneapolis, U of MN East Bank and the airport. A few take aways:
* Stations can be constructed within the St. Peter sandstone beneath the Platville limestone layer in all the locations.
* In downtown the sandstone layer is deeper (100') compared to just 50' at the airport. That would put downtown Minneapolis stations into the water table.
* The report states that the sandstone is relatively easy to dig through and that the limestone layer would act as a roof potentially resulting in comparably low costs to dig the tunnel compared to other geologies.

The report does seem quite dated considering the data is 30+ years old. In particular, it spends a lot of time discussing the potential design of underground stations as if there were few good examples to look at when the report was written. So many subway stations have been built over the years likely providing many examples of good station design. Also, I imagine modern technology would allow for more precise measurements of the sandstone such as with the Central City storm water tunnel.

[StandishGuy]

One more thing... The downtown subway tunnel described in the document takes a route I've never heard of previously. There would be 5 underground stations in/ near downtown Minneapolis largely following Marquette Ave. This includes a Central Library, Warehouse District station, 7th & Marquette/ IDS Station, Convention Center and the Minneapolis Institute of Arts. The line would end at 29th & Nicollet. The Metronome station would have been above ground. It's pretty dramatic how both the route and above ground construction ended up so different than this report.

[mattaudio]

Back in the Minnescraper days, possibly before Target Field, I pined for a 6th Street tunnel.

It would have leveraged the Target Field and Metrodome excavations for eastern and western portals.

And, because it was already full unreality, I suggested a two-level tunnel akin to Market Street in SFO or the F tunnel which recently inaugurated LIRR to Grand Central. LRT on one level, heavy rail on another. Approached on both ends via the NP #9 bridge, NP bridge north of Lowry, and the 4th St Viaducts corridor to create a through-running loop for commuter and intercity trains between Northtown Yard and the Midway/Merriam Park subdivisions to St. Paul.

[MinneapBliss]

That awesome routing was one of my takeaways, too...stations underneath the MIA, IDS, central library, among others. If only.

I would love to believe there's enough political will to build a deep tunnel under downtown Mpls. I'm doubtful, but would love to be proven wrong! Another challenge with the deep tunnel is how much more existing track you'd have to replace/regrade to achieve the maximum grade % (or less) for trains' approach to a new station.
Maybe we could sell the excavated St. Peter sandstone as frac sand to offset the cost? That's sarcasm...mostly.

[mister.shoes]

Back in the Minnescraper days, possibly before Target Field, I pined for a 6th Street tunnel.

It would have leveraged the Target Field and Metrodome excavations for eastern and western portals.

And, because it was already full unreality, I suggested a two-level tunnel akin to Market Street in SFO or the F tunnel which recently inaugurated LIRR to Grand Central. LRT on one level, heavy rail on another. Approached on both ends via the NP #9 bridge, NP bridge north of Lowry, and the 4th St Viaducts corridor to create a through-running loop for commuter and intercity trains between Northtown Yard and the Midway/Merriam Park subdivisions to St. Paul.

I had your 6th Street tunnel idea in mind the whole time I was writing mine. As amazing as a true deep bore would be, I think what I suggested could be pulled off with cut and cover. Ah well.

[pannierpacker]

How exactly would these staircases work in a 'deep bore' scenario? If the stations are 100' below the surface, I'd imagine that the stairs would need to wrap quite a few times to fit into a small portal? In that event, wouldn't such a stairway feel long/circuitious/dark ? Are there any examples of staircases this deep in other public transportation systems around the world?

[Oreos&Milk]

Ok I like the idea of an underground LRT tunnel.. I think of the possibilities! An underground connection directly into the US Bank Stadium, A direct connection to the Hennepin county courthouse tunnel/skyway corridor, An merged Hennepin/Nicollet Mall station that provides a pedestrian-only corridor in both directions to each street, and direct tunnel access to the Ramp B which will provide easy downtown parking and then ride access. For example taking the train to the farmers market when you already have a downtown monthly parking membership.

However wouldn't it be cheaper or better idea to make the streets disconnected or tunneled under the train one at a time? Maybe even it's just shutting them down at the train crossing during rush hour? I know downtown traffic can be pretty bad but why would we tolerate slowing down our public transit (a train of 300+ people) to let some 22 people in single occupancy cars go first?

I mean Nicollet, Hennepin 2nd & Marq, Park , and Portland could all be tunneled one at a time. Then close down half of the rest during rush hour and the rest are deprioritized to the max and let them eat cake in traffic.

EVEN if we did build a tunnel like people suggested it would have to be AT LEAST a 3 track tunnel that way we can close one track down for repairs and maintenance and maintain the other two tracks in normal operation. Yes, that means have 3 track stations so we don't have to do the whole bus bridge thing every few months or few years for repairs. Do we honestly think we are able to make THAT level of investment in our system to ensure we have a quality level of service?

If not wouldn't roadway tunnels be a better option?

[Trademark]

Ok I like the idea of an underground LRT tunnel.. I think of the possibilities! An underground connection directly into the US Bank Stadium, A direct connection to the Hennepin county courthouse tunnel/skyway corridor, An merged Hennepin/Nicollet Mall station that provides a pedestrian-only corridor in both directions to each street, and direct tunnel access to the Ramp B which will provide easy downtown parking and then ride access. For example taking the train to the farmers market when you already have a downtown monthly parking membership.

However wouldn't it be cheaper or better idea to make the streets disconnected or tunneled under the train one at a time? Maybe even it's just shutting them down at the train crossing during rush hour? I know downtown traffic can be pretty bad but why would we tolerate slowing down our public transit (a train of 300+ people) to let some 22 people in single occupancy cars go first?

I mean Nicollet, Hennepin 2nd & Marq, Park , and Portland could all be tunneled one at a time. Then close down half of the rest during rush hour and the rest are deprioritized to the max and let them eat cake in traffic.

EVEN if we did build a tunnel like people suggested it would have to be AT LEAST a 3 track tunnel that way we can close one track down for repairs and maintenance and maintain the other two tracks in normal operation. Yes, that means have 3 track stations so we don't have to do the whole bus bridge thing every few months or few years for repairs. Do we honestly think we are able to make THAT level of investment in our system to ensure we have a quality level of service?

If not wouldn't roadway tunnels be a better option?

There's no way that a three track tunnel will be built. No tunnels built in the US or Canada that are new are being built as triple track. It can just be single tracked when the rare maintenance needs to be done, or if overnight service isn't brought back maintenance can be done then. Triple track will add a ton of cost with extremely small operational benefit.

[Silophant]

How exactly would these staircases work in a 'deep bore' scenario? If the stations are 100' below the surface, I'd imagine that the stairs would need to wrap quite a few times to fit into a small portal? In that event, wouldn't such a stairway feel long/circuitious/dark ? Are there any examples of staircases this deep in other public transportation systems around the world?

There's a few ways to go about it. The Peachtree Center MARTA station in Midtown Atlanta is 120' below ground, and just has extremely long single-stage escalators. I believe it's more common, though, for extremely deep stations to have a lot of stacked escalator stages. There was one memorable one in Barcelona where I got off one train and rode up five or six switchbacked escalators just to get up to the other platform, though not memorable enough to remember which station it was.

The Portland Max station serving the Oregon Zoo is the deepest train station in the Western Hemisphere, and is served only by elevators (presumably there's an emergency staircase somewhere), but I think they can only get away with that because it's a relatively low-use station - that wouldn't fly during downtown rush hours.