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Subway train elevator

Raise/lower train between tunnel and elevated tracks at station
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The idea:

Envision a subway station where elevated tracks (say, 30 feet above ground) enter from one side at the platform level. The tracks adjacent to the platform sit atop a big 10 foot wide x 450-600 foot long elevator. Between the platform and the train are automated sliding doors like some subway stations have to keep people from falling in front of trains. The train enters the station, stops when aligned with the doors, and passengers enter/exit. When the doors close, the elevator upon which the tracks and train sit lowers it to the tunnel (say, 20-40 feet underground), whereupon the train continues to the next station. As soon as the train clears the tracks sitting on the elevator, it returns to the platform level to await the next train.

Obviously, lots of safety interlocks are in place... the tracks leading to the elevator are automatically de-energized unless the elevator is in place and secure at the same level as the tracks. The elevator itself can not move vertically if the tracks on it and the tracks leading to it are both energized, and the tracks leading to it can't be de-energized when there's a train detected on them.

Why build such a device? To enable a subway to run aboveground to some point for aesthetic, economic, or other reasons, but vertically transition to underground operation for the remainder of the trip.

Where would such a device be appropriate? South Beach (Miami).

Background: at the moment, Miami-Dade county is exploring the possibility of extending some form of rail mass transit from the mainland to South Beach. The two realistic options are surface light rail and underground subway. Miami Beach has more or less eliminated elevated guideways as an option due to noise and aesthetic reasons (people paying $500/night for a hotel room in a quaint art deco hotel wouldn't be happy about a loud train rumbling by 20 feet outside their window). Light rail is popular with tourists because it gives a nice view, and popular with the county government because it's cheap. However, it's mostly useless to (and generally opposed by) residents because it would be too slow to be worth using, and would basically make traffic along the route much, MUCH worse than it is now. On the other hand, a subway would be perfect for residents (speed), but would make the trip itself a lot less enjoyable (think: dark tunnel vs view of water and palm trees).

The ideal scenario would be extending Metrorail above ground along the causeway to the first stop in South Beach itself (preserving the ambience for most of the trip), then dropping it below ground for the last mile. The problem is that there's really no good place to put the 2-3,000 foot transition zone needed to take it underground. Economically, it would probably be cheaper to blast down a 60 foot path from Alton Road (to the west) and Washington Avenue (to the east), but politically it would be next to impossible.

Apparently, the island itself is geologically stable enough to permit "cut and cover" construction just below street level, but a tunnel under the bay would have to be bored fairly deep, and transitioning from aboveground to underground along the causeway would cost a LOT more than just going underground on the mainland and boring the whole thing underground all the way.

miamicanes, Feb 19 2003


       How fast would this elevator need to be? If it takes 30 seconds to move from above ground to underground, that's 30 seconds added to your trip. Also, it would need to have an enormous capacity, as subway trains are extremely heavy and large.
andrewm, Mar 06 2003

       I'm not familiar with Miami, but the trains in NYC go from being subways to being els using good, old-fashioned technology (viz., a ramp). Why wouldn't that work down there?
DrCurry, Mar 06 2003

       Basically, what I envision is a platform that's around 610 feet long and 12-14 feet wide, made out of some strong, but lightweight material (titanium?), surrounded by vertical supports that would be pushed against by wheels surrounded with some kind of shock-absorbing material like rubber to keep it vertically aligned. Imagine, for a moment, pairs of cement pillars a few inches away from the platform on both sides. Two wheels are mounted parallel to the long direction of the platform at each pillar (in other words, if the wheels were spun, they'd spin in the same direction the train travels or the opposite direction), making contact with the "front" and "rear" sides of the pillar. Then, in between the passenger door areas, there'd be recessed areas, and another pair of pillars (one on each side of the platform) that would also be pressed against by wheels mounted on the platform, but THOSE wheels would be perpendicular to the direction of the train's travel. In other words, there are wheels spinning parallel to the train's wheels to stabilize the platform along the long axis, and more wheels spinning perpendicular to the train's wheels to stabilize it along the narrow axis.   

       The actual lift would be either lots of cables along either side, or a lot of hydraulic cylinders beneath the platform. Once again, the general idea is that the weight gets distributed among them, so each one only has to directly contribute to lifting a fraction of the combined total weight of the platform, train, and passengers. That's part of the reason why the platform itself upon which the tracks were mounted would have to be something ultra-light, but also ultra stiff like Titanium... so if one hydraulic cylinder or cable pair weren't quite doing its share of the work, the weight would just get shifted to a neighboring cylinder/cable.   

       Taking safety and interlocks into consideration, I believe a 2-3 minute total round trip time for the platform is entirely do-able. With 5 minute headway (more or less the normal design spec for subways), and a minute for passengers to exit and enter the train itself, the platform would STILL have at least a minute or two to spare between the time it returned to the proper position for the next incoming train and the train's actual arrival.   

       The 45-60 second vertical trip would be a downside, but I think the sheer novelty and coolness of it would pacify all but the most jaded residents.   

       As for why it can't just go underground gradually, there's no possible route that isn't lined with dense, unfathomably expensive real estate on both sides. Screw neighborhood preservation... we're talking about hundreds of millions of dollars worth of prime property-tax generating real estate whose value would be *decimated* by close proximity to a noisy steel-wheeled train roaring by on its way underground over the span of 4 blocks. It simply won't happen. The proposed elevator/station happens to sit literally 30 feet from where the causeway reaches the island. I guarantee that there's absolutely no way in *hell* Miami Beach will *ever* agree to let an above-ground steel-wheel train operate more than a block away from the causeway. If dropping it vertically underground at a station adjacent to where the causeway meets the island isn't feasible, it'll have to be TOTALLY underground by the time it reaches the island.
miamicanes, May 13 2003

       [Admin: renamed idea 'Subway TRAIN elevator' to 'Subway train elevator'.]
st3f, Feb 29 2004

       Ok, one problem with where you think it would be most ideal....southern Florida has an unusual water-table that prohibits the building of basements even...let alone subway tunnels. That's why Metrorail is elevated. But the idea would make sense in plenty of other areas.
Raakone, Aug 02 2004

       Actually, the water table ISN'T the reason why Florida homes lack basements. Economics and climate are. "Up north", it's necessary to dig a hole before building a house so the foundation sits on ground that's deep enough to never freeze. Since you have to dig a 4-6 foot deep hole one way or another, the marginal cost of turning it into cheap, useful (if damp and substandard) space is fairly low. In Florida, there's no need to dig down, so digging the hole would be 100% additional cost. Unless you're dealing with height limit and you've maxed out your home's footprint, there's really no good reason to go down instead of up if your only goal is a bigger house.   

       As for the water table... well, below the concrete, New York, Boston, Chicago, Washington, Hamburg, London, St. Petersburg (Russia), and just about every other big city in the world with subways is a wet, soggy swamp. Lower Manhattan is probably the soggiest, most unbuildable piece of land in America... yet they still managed to build (what was briefly) the tallest building in America, multiple subway tunnels, and 7+ story deep basements there. In Boston, some of the "Big Dig" tunnels were precast, lowered into a pit, and rammed into the muck with hydraulic jacks. They scooped the muck out of the inside, put the next precast section in place, and kept ramming. It's just that up until now, land in Miami wasn't expensive enough to merit the cost of going underground.   

       However, this idea is now semi- moot. The chunk of land I had in mind for the station (northeast corner of 5th Street and Alton Rd) is now being developed into what would have been a perfect vertical big-box plaza to build above the station. Oh well. I guess they could always route Metrorail to AA Arena, continue to the port, then go underground and put the first station deep below South Pointe before heading north below Washington Ave, then Pennsylvania Ave (a block west of Washington Ave) and ending with another huge Dadeland Station-type plaza/station where the northeast Lincoln Road parking lot is now.
miamicanes, Jan 31 2006


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