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Anon256

Even if you don't use them in regular service, multi-way connections like these are very useful in cases of service disruption. On the IND lines in Manhattan, the MTA often deals with construction by routing 8th Ave trains onto 6th Ave or vice versa. In other parts of the system without such flexibility, construction can lead to long stretches being bustituted when even a very localised construction project prevents the line from running through.

This sort of flexibility also allows the system to easily adapt to changing ridership patterns. For example, during the 1980s, Brooklyn's Brighton line was served only by trains to Nassau St or 6th Ave in Manhattan, but the rebirth of Times Square and other points on Broadway led to changes in passenger demand, and now most service on the Brighton line is provided by the Q train to Broadway. The extreme flexibility of DeKalb junction made this change possible. Washington DC would probably be better off today if it had constructed short connecting curves to allow some Orange line trains to turn right before Rosslyn and run into downtown via Arlington Cemetery and the Yellow Line bridge. These would not have been necessary when the system opened, but the densification of the Ballston corridor has filled the Orange line to capacity.

Complicated grade-separated junctions can be expensive and are worth a cost-benefit analysis, but there definitely are benefits.

anonymouse

Anon256: for occasional diversions, you can just have a simple diamond crossover, rather than the fancy grade-separated junctions at Camden Town or West 4th. And at West 4th, the flexible layout means that the "through" routes for the southbound F and northbound C/E actually have to take a diverging route through a switch, with all the increased wear on the switch points that that implies.

Jarrett: I think the real reason behind building in this flexibility is not to be able to do something like the Northern Line where there's trains from every branch to every other branch, but rather to ensure it's possible to switch a service pattern of A-B and C-D to A-D and C-B if some years or decades in the future, the relative demand on the branches means that that's the more effective way to run the service.

Alon Levy

There definitely are benefits to flying junctions, but on the IND, the costs outweighed them. The First System went way over budget and behind schedule, which together with the Depression is why they didn't start building the Second System right away.

What I've read of the Northern Line is that the plan is to go to a configuration requiring a transfer at Camden Town, which would increase capacity.

francis

I wonder if that quirk of Mornington Crescent is the cause for the game of the same name...

Tom West

Slightly off-topic, but at Euston, the branch which goes west is actually on the eastern side (and vice versa)! This is a good exmmaple of why topographic maps (like the Tube's) can be superior to geographic accurate maps.

Pete

The problem of branching halving frequency was solved for the Bakerloo Line when the Jubilee Line opened incorporating the Bakerloo's Stanmore Branch. This enabled the frequency on the remaining Queen's Park (via the mainline terminals of Marylebone and Paddington) t be doubled. Service on the Queens Park was also projected along the Network Rail Watford 'DC' line to Harrow & Wealdstone and the small profile tube trains share tracks with main line stock.
http://maninblue1947.files.wordpress.com/2009/05/052-g-stonebridge-park-10-04-09.jpg?w=470&h=330

John W

I lived a couple of stops north of Camden for a few years, and I quite liked having that flexibility. Much simpler just to wait a couple of minutes rather than dash through Camden Town station and try to figure out which platform the train would be on (iirc southbound trains for Charing Cross or the City could be on either platform, depending on which line it was coming south on; so you'd get midway through the station, look at screen with next departure and realise you had to go back to the platform you were on). Would still try to game the system, though: if it was more than a 5 minute wait for the train I wanted, I'd take the first one and see if I could save a couple of minutes by transferring.

According to TfL, there are plans to deal with the southern branching, though no mention of any changes at Camden: http://www.tfl.gov.uk/corporate/projectsandschemes/18091.aspx

And if this goes ahead, it actually will be a proper branching at Kennington rather than what's effectively a T-junction:
http://www.thisislondon.co.uk/standard/article-23895421-battersea-power-station-offers-pound-203m-for-northern-line-upgrade.do

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the firm

Jarrett is now in ...

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