Submitted by walkallover1991 t3_ydxsw5 in washingtondc
plutopius t1_itv4siz wrote
Reply to comment by dadonnel in Metro studying Silver Line Express service by walkallover1991
Right? The two track system has been a known issue with metro. Adding a new line would've been the perfect opportunity to add additional tracks.
22304_selling t1_itv9a5m wrote
> known issue
What issue? The vast majority of metro systems around the world use two tracks.
>Adding a new line
On what right-of-way?
plutopius t1_itvet4u wrote
The issue is that when there is a problem with one train/station, the whole rail line has to stop because there's no way for functional trains to pass.
The rest of the world has nothing to do with this. I'm sure there are other train systems that have a similar problem.
The new line I am referencing is the Silver line past the Blue and Orange stops, not a right of way.
Cythrosi t1_itvq455 wrote
What the rest of the world does is highly relevant, because running a railroad doesn't magically change physics and logistics because a border was crossed.
Most other systems make effective use of signaling and crossovers to maximize a two track configuration to allow quick bypass of problems. They also work to provide effective line density and connections to allow people to simply pick another path to their destination. Running quad track/express systems really only becomes beneficial when you have heavy density and ridership (we have neither of those currently). The money spent on quad track/express service can often be spent providing more service in a parallel corridor which both serves more people/neighborhoods and allows relief off lines when there may be a major issue on another line.
plutopius t1_itvwb78 wrote
With our "all roads lines downtown" system, adding parallel lines would just cause bottleneck once they converge in the city. What you're saying with parallel lines is relevant for a grid system, which we do not have.
Cythrosi t1_itw80uo wrote
Not really. Look at London. Its primary focus of most its lines are to pass through the core of London. It is aided though by a massive amount of connections and interchanges that allow immense flexibility. Between the multiple lines with connections at key points, the Overground, the Elizabeth Line, DLR and a robust bus network, a problem on one line doesn't criple the network.
Adding a 4th trunk line (and more in the future even) through DC with more connections and transfer opportunities would do more to improve Metro service than express tracks ever could. Express service only really makes sense when you have the density for it. DC is not dense enough (and probably never will be) to justify the cost of adding express tracks and services on the Metro lines.
plutopius t1_itwc41k wrote
>DC is not dense enough (and probably never will be) to justify the cost of adding express tracks and services on the Metro lines.
Overall I agree with this. There no need for express in the city. But an express to the airport could've been done with better planning. After-the fact is useless.
Also, much of London Underground uses 4-tracks, which kinda derails (pun intended) what you're saying.
classicalL t1_itx86am wrote
Of course a 4 track everywhere system is better.
The question is do you want a 4 track system with half as many stops or a 2 track system with twice as much length?
It isn't quite linear scaling in cost, but you still need to physically make all the stations and platforms bigger, lay twice as much track, have twice as many signals and so on. You nominally get half as many stops and distance in your budget.
Generally the observation is that a dense network of 2 track systems is best. A good example of this is basically London. Nothing is quad tracked, but if a segment goes down you can go around it. They just built an ultra-modern cross London train (Crossrail/Elizabeth Line) it is 2 tracks.
For the WMATA system the step to add that is the "separated blue line" proposal. The system would benefit from a 2nd east-west main line though the city. Ideally touching all the lines. This allows transfers to get around a broken train or other issue in the core. It doesn't help you in the tails of the system, but they have less riders anyway.
Interlining is something that the WMATA system does a lot of that is unusual which increases the dependencies between them. In a separate blue line system Green basically has 2 southern branches (yellow) and 1 northern. Orange has two east and west branches (silver). Blue is on its own. Red is on its own.
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