Green Line / Central Corridor construction thread (archive)

[FISHMANPET]

I think there's been official squashing of the idea of a University stub line, we'll all just have to wait until 2014 like everybody else.

[mulad]

I think much of the catenary on campus will only have a single wire, like segments in downtown Minneapolis on Hiawatha. The trains will only go 25 mph or less along much of that stretch, which doesn't need the two-wire setup. It'll be faster on Washington Ave Bridge, though.

[talindsay]

Just a minor point, but I think if it's single wire it's not catenary - the term refers to the way the top wire hangs naturally (in a catenary shape), with varying lengths of support wire binding the lower to it, to provide a flat, straight path for the lower wire.

[mulad]

Yeah, some more generic terms are "overhead wire" or "overhead lines".

[kirby96]

I'm a nerd. I think that's interesting. I know nothing about trains. I suppose that's done to hold it in a straight line with out requiring significant tension?

[twincitizen]

I think there's been official squashing of the idea of a University stub line, we'll all just have to wait until 2014 like everybody else.

Agreed. Even if it was physically/technologically possible, Metro Transit does not have that in the labor budget. The timeline to get rail operators hired and trained is probably very closely aligned with the construction schedule. To think there's some miracle chance that trains will be running in revenue service before May 2014 is complete fantasy. Sorry guys.

[Tom H.]

I'm a nerd. I think that's interesting. I know nothing about trains. I suppose that's done to hold it in a straight line with out requiring significant tension?

To be precise (I'm a physicist), it would take infinite tension to pull a hanging wire perfectly straight (or, similarly, a massless wire or zero gravity). Mathematically speaking, a straight line is the limit of a caternary as tension goes to infinity. Wikipedia has a nice derivation of the analytic form of the caternary curve (a hyperbolic cosine).

[commissioner]

Anyone know if the green line is still on schedule with the rain we've had and when is the Hiawatha lrt bike trail supposed to reopen? Thanks in advance!

[FISHMANPET]

Line opens next year not this year. Rain right now doesn't really matter.

[commissioner]

I knew it was opening next year but thanks anyway fishmarket

[kirby96]

I'm a nerd. I think that's interesting. I know nothing about trains. I suppose that's done to hold it in a straight line with out requiring significant tension?

To be precise (I'm a physicist), it would take infinite tension to pull a hanging wire perfectly straight (or, similarly, a massless wire or zero gravity). Mathematically speaking, a straight line is the limit of a caternary as tension goes to infinity. Wikipedia has a nice derivation of the analytic form of the caternary curve (a hyperbolic cosine).

Yeah, I get that. Any mass will be subject to the force of gravity, and thus 'hang'. Should have said, "sufficiently straight." guess i was more surprised that the tolerance of the train is tight enough to require what looks a little 'rube goldberg-ish' to the uninformed observer. Thx!

[talindsay]

Yeah, I get that. Any mass will be subject to the force of gravity, and thus 'hang'. Should have said, "sufficiently straight." guess i was more surprised that the tolerance of the train is tight enough to require what looks a little 'rube goldberg-ish' to the uninformed observer. Thx!

It depends primarily on the speed of the train, and also on whether it needs more than one pantograph for power. The TGV trains in France have two pantographs - one at the front and one at the rear - and so apparently catenary tension was one of the biggest engineering problems limiting the speed of the trains. The lead pantograph produces a wave in the power line, which disrupts power to the trail pantograph if not precisely aligned for the distance between pantographs and speed of the train. All the LGVs (high-speed lines) in France have carefully-constructed catenary wiring to control for this, supposedly.

The main thing though is that catenary wiring is functionally a requirement for non-rigid friction-contact power systems - the power wire has to be very close to flat and very precisely positioned, with adequate tension, for the pantograph to remain in contact with the wire: too high and it loses the connection, but too low and it introduces a whipping waveform into the wire which also loses the connection. Trolleys didn't have this problem because the wheel on the trolley pole hung on the wire, floating up and down with the wire - but more importantly, because trolleys were so slow that such a system basically worked. It's worth noting, however, that trolley poles become disconnected so frequently that any trolley driver quickly became an expert at reconnecting the pole.

[mulad]

Eep, getting into the weeds a little -- London-Paris Eurostar trainsets have two pantographs on them and both are used. Regular TGVs are half as long and only use the rear pantograph, though two TGVs are often coupled together, each using the rear pantograph. Anyway, I had been thinking of posting a video showing how everything jostles around using a TGV video or two, so I may as well post something. Whatever train you're talking about, the second pantograph has a tougher time since it has to deal with some of the wave action set up by the first. You can often see sparks flying from the second one, particularly at night, while the leading pantograph does a much better job of staying in contact.

The pantograph (well, half-pantograph) is also spring-loaded and will rise and fall a bit as it follows the wire between the fixed points where the wire is mounted. The rising and falling probably isn't quite as pronounced for LRT, partly since the towers are closer together for that.

Here are a couple of videos with good examples from YouTube user dashloc, who is a TGV operator (you'll probably have to click through to view these on YouTube in order to get the full effect, though):

[mulad]

I took the 16 this evening to get some handle on catenary progress. Some mounting hardware is being installed on the catenary poles between Lexington and Snelling. It looks like a single set of wires has been strung most of the way from Fairview to Snelling, though it's not tensioned at all yet. Wires for both tracks are pretty much continuous from Fairview Avenue to Harvard Street on the UMN campus, mostly tensioned, but some not. The single-wire overhead line (not "catenary") appears to run from just "east" of the Stadium Village station (the corner of Huron/23rd and the UMN transitway) into the campus. Other than that, catenary only exists from the West Bank station westward to the junction with the Blue Line.

I took a few photos near the U. Still under construction, this turn at University and 29th Ave will probably become the craziest mess of wires on the whole line:


Here's the intersection at 29th Ave and 4th Street SE, between University Ave and the UMN transitway.


The turn from 29th to the UMN transitway:


Tracks and loose catenary along the transitway at 25th Ave:


Opposite direction:


Single-wire overhead line north/east of the Stadium Village station:


I saw a few dozen barriers set up along the guideway on Washington Avenue, and was worried that it was because people were driving all over it, but it looks like they're just protecting open holes where some access panels have been removed.

[seanrichardryan]

University/ STP gets an elegant green cantenary pole and MPLS gets standard galvanized? what gives?

[trkaiser]

IIRC, St. Paul ponied up additional cash for enhancements along its chunk of the line.

[talindsay]

IIRC, St. Paul ponied up additional cash for enhancements along its chunk of the line.

Winner winner chicken dinner. St. Paul came up with the cash.

[VAStationDude]

I believe Mulad's first picture at 29th Ave and University shows the fancier poles east of 29th which is still Minneapolis. Personally, I think the poles along Washington transit mall fit nicely and the galvanized work well along the transitway since it is an industrial area.

[twincitizen]

http://finance-commerce.com/transit/201 ... continues/

93% complete. Intermittent road closures ahead for downtown St. Paul and Wash Ave trench

[commissioner]

The dark poles go to just past the prospect park station toward Mpls. While both sets look neat, I'm suprised they didnt go with the same color all the way through, maybe the U wanted it that way?