Round-the-corner at Rosslyn

In this post Sand Box John posted a diagram showing one conceptual route for the M Street Subway, and one of the key features of the map is the "dotted line" connection between the C Route and the K Route west of Rosslyn, presumably to allow in-service trains to run directly from Arlington Cemetery to Court House and vice versa.

In this thread there is much discussion about the supposed safety problems with using the pocket track at D&G Junction to reverse the Silver Line service and also some discussion on the potential rostering problems with train crew who have to run the end-to-end Silver Line service.

Putting two and two together, this makes me wonder if a round-the-corner connection at Rosslyn would solve some of the problems that the Silver Line might have east of there by allowing part of an enhanced Orange Line service ex-Vienna to be routed down the C Route towards Alexandria, extending the existing Yellow Line rush hour service to Franconia-Springfield to off-peak periods to make room for the round-the-corner trains towards Alexandria, and using the remaining capacity of the C Route east of Rosslyn for the entire Silver Line and the leftover portion of the Orange Line service. East of Stadium-Armory, this might allow the entire rush hour Orange Line service to Largo to be replaced entirely with the Silver Line service, which would simplify the service pattern somewhat.

On the surface it seems conceptually simple and would add a lot of flexibility to the network west of the Potomac, but I'm sure I'm missing something obvious that doesn't make it viable. What does the forum think?

What you are talking about is the proposed interline connector at Rosslyn which would bypass the Rosslyn station with connecting tunnels that would allow trains to go from the Orange/Silver line to the Blue line through Arlington Cemetery. The Rosslyn bypass interline connector is included in the Metro Momentum 2025/2040 strategic planning document released in January and was incorporated in several of the viewgraph presentations of the Technical Advisory Group (TAG) meetings (which can be found on the planitmetro.com website).

The other interline connector concept that emerged from the TAG review is at the Pentagon station stop running from the Blue Line to the Yellow Line heading across the river with a new second Pentagon station located along the interline connector. north of the current station. These 2 interline connector would allow for a new line originating from Vienna or Ashburn/Dulles to skip Rosslyn. go through Arlington Cemetery and then north across the Potomac into DC across the bridge. Or with just the Rosslyn interline bypass, to create a Virginia only line that run from the Silver line to National Airport and down to Huntington or Franconia-Springfield.

Traffic capacity considerations are very much an issue with these concept however. Any trains that are added to the Blue/Yellow line from the Pentagon to Old Town take away from peak number of Yellow line trains that can be run into DC. Additional trains from west of Rosslyn that run SE to the new Pentagon stop and then across the river into DC would merge with the Yellow/Green line which has its own capacity constraint concerns. The Greater Greater Washington blog had several good postings discussing the capacity constraint tradeoffs of possible alternate routings. Building the interline bypasses at Rosslyn or at the Pentagon with a new station would be challenging and pricey projects.

Ok, found the links to several of the GGW posts: Metro stuffed full at Rosslyn; Metro Beyond 2025 Part 1 and Metro Beyond 2025 Part 2.

Thanks for posting those links; they were quite interesting. The most puzzling point made in the posts was that the maximum capacity of the route east of Rosslyn is 26 tph. Sand Box John previously said that the entire system was designed and built with a minimum headway of 90 seconds, which allows up to 40 tph in ideal circumstances (which never happens).

The capacity concerns you mention are why I suggested increasing the service ex-Vienna and diverting it towards Alexandria - I would expect that there is at least some unusable capacity on the routes west of Rosslyn and south of the river because of the capacity constraints beyond those points. My assumption was that you could increase the service on both routes without affecting the service through the District.

I don't understand why anyone would push for 40 tph. sounds great in theory but it will never be executed right. it will probably turn out into a disaster. this is metro we're talking about.

i'm also not sure if wye switches would solve these capacity issues in the long run, looks like a band aid fix that will only solve issues in the short run. also if there are switch malfunctions it will cause some nasty delays...

it would be great if they would eliminate the interlining and have unique tracks for each lines. not only would it increase coverage but it will add redundancy in the system. too bad it will cost billions of dollars and no one will ever pay for it. one can dream though...

"YOLO"
I don't understand why anyone would push for 40 tph. sounds great in theory but it will never be executed right.

WMATA has run 90 second headways in the past when they had sufficient rolling stock to do so. They have had a rolling stock shortage sense the C Route was opened to Huntington on 12 07 1983.

It will probably turn out into a disaster. this is metro we're talking about.

The problem is the suits that are running the railroad now have forgotten how to do it because they no longer have to tools to do it.

Much of WMATA's capacity issue can be solved by procuring more rolling stock. And I am not talking about the 220 "Fleet Enhancement" cars that are optioned in the Kawasaki contract to allow for all 8 car trains during peak running at 150 second headways that is WMATA ultimate goal. Those 220 cars will only increase the fleet size to cut headways from the present 180 second headways to 150 seconds. Using that fleet enhancement figure, WMATA would need increase the total fleet by roughly 500 cars after all of the Kawasaki options exercised to have a fleet large enough to run all 8 car trains at 90 second headways during peak.

I'm also not sure if wye switches would solve these capacity issues in the long run, looks like a band aid fix that will only solve issues in the short run.

The Ys would add operational flexibility to the system that now does not exist.

Also if there are switch malfunctions it will cause some nasty delays...

You also seem to forget that ever time a train heading through a junction that is going to a final destination that is different then the previous train a turnout is thrown, same happens when trains relay at a terminals.

It would be great if they would eliminate the interlining and have unique tracks for each lines. not only would it increase coverage but it will add redundancy in the system. too bad it will cost billions of dollars and no one will ever pay for it. one can dream though...

You are falling for the propaganda the media has been parroting from WMATA for the last 10 years. The first time I heard WMATA claim the Rosslyn portal can only accommodate 26 trains per hour, I thought to myself, who's ass are they pulling figure out of. The train control and signaling system is designed to accommodate 40 trains per hour. The amount of money need to increase the fleet size to accommodate 90 second headways would be small fraction of the cost of the entire M Street subway.