The Montgomery County Planning Board toured the Bethesda Tunnel and the Interim CCT connection to the Rock Creek Trail yesterday to examine CCT cost issues. MTA and Montgomery County DOT and M-NCPPC staff briefed them on costs of rebuilding the CCT with the Purple Line.
Route of the Nov. 3 Planning Board tour at Bethesda
Source: Tour agenda and MTA CCT cost report (a pdf file)
Several dozen neighborhood residents also turned out for the tour, many carrying “Save the Trail” placards. Katherine Shaver was there to report for the Washington Post. Planning Board Chair Francoise Carrier reminded those present that the purpose of the tour was for the Planning Board to ask questions of the Purple Line planners. She invited the public to present comments at the Nov. 17 Planning Board work session.
Planning Board Chair Francoise Carrier addresses the public.
I’ve already posted that is important we not get tunnel vision and put too much focus on the Bethesda Tunnel while losing sight of the bigger picture for the whole trail. But I was on the Bethesda part of the tour, and would like to offer comments on several issues at the Bethesda Tunnel of interest to trail users. I’m not advocating hard for any one idea yet – I’m still trying to get a clearer picture on what the realistic choices are to make both the Purple Line and the CCT work well here:
1) Cost to put CCT over the Purple Line through the tunnel.
MTA Purple Line project manager Mike Madden stated that much of the cost and risk to dig to lower the Purple Line below the current grade, necessary to fit a trail overhead, is associated with stabilizing 35 beams that support the Apex Building. He also said that even if the Purple Line is built at the current grade without the CCT, there still will be some beams near the west end of the tunnel that will require stabilizing. MTA does not know yet how many beams would still require stabilizing even if they do not dig.
The cost of building the trail over the Purple Line in the tunnel is estimated to be 43% of the total estimated $103M trail cost. (Source: Tour agenda and MTA CCT cost report.) But that cost includes the cost of stabilizing all of the 35 beams. We need to subtract the cost of stabilizing the beams that must be done even if we do not dig, from the cost of stabilizing all 35 beams if we do dig, to know the stabilization cost that is due to the CCT.
Adjusting the cost to reflect the cost difference for stabilizing the beams will bring the CCT cost estimate down a little. And the fact that MTA does not yet know how many beams must be stabilized if we do not dig suggests they have not done enough exploration yet to have a firm cost estimate. We should have better information before we make decisions based on cost.
2) Fitting a pedestrain trail alongside the Purple Line.
WashCycle raised the question in recent blog post comments whether it might be possible to have a narrow trail alongside the Purple Line in the tunnel, without digging. The tunnel under the Apex building west of Wisconsin Ave. is wide enough to permit this – plans already call for pedestrian access from the west tunnel portal to the Purple Line platform and Metro elevators near the middle of the tunnel. But the tunnel under the Air Rights building at the east end is narrower, only 32′ wide from wall to wall. Recent Purple Line profile drawings show two light-rail tracks have a typical 29′ wide profile. But these profiles are for unconstrained spaces where the Purple Line runs at speed. It may be acceptible to reduce the separation distances between tracks and between the tracks and the side structures (i.e. poles to support the catenary wires) in the tunnel where vehicle speeds will be very low – perhaps to achieve a profile as little as 24′ wide which would leave room for an 8′ wide path in a 32′ wide total space. But you would need to be able to use all of the tunnel width from wall to wall, with no setbacks from below-grade foundation structures.
I raised this issue with MTA engineers at the Nov. 2 Open House at the National 4-H Education Center in Chevy Chase. They had not considered this yet, but agreed it should be looked at seriously. They had two concerns that might wreck the idea: 1) The tunnel width under the Wisconsin Avenue bridge might be less than it is under the Air Rights Building, and 2) The tunnel has a curve, which will require a wider spacing between tracks to allow for the transit vehicle “overhang” on the curve.
During the Nov. 3 tour we saw the tunnel under the Wisconsin Avenue bridge. Slopes down from the bridge abutment structures on both sides of the tunnel do indeed pinch the tunnel to be narrower than under the Air Rights Building. But Mike Madden explained that these were only dirt slopes, covered with concrete for erosion control. The abutment structures that support the bridge are set well back. The slopes can be cut back, and retaining walls can be used for the erosion control without disturbing any bridge structures. This could make the tunnel wider under the Wisconsin Avenue Bridge than under the Air Rights Building.
It was apparent during the walk through that the curvature of the tunnel under the Air Rights Building was only at the west side of the building and very slight. It appears likely that any allowance required for vehicle “overhang” at the curve would be slight. Mike Madden also stated that the walls of the Air Rights Building tunnel were structurally stable and extended deep enough so that they would not need to be modified, even if digging was needed.
Profile of Purple Line with CCT under the Air Rights Building
Source: Tour agenda and MTA CCT cost report (a pdf file)
It therefore appears to be very feasible to have a 6-8′ wide walking trail east through the tunnel from the Purple Line platform and Metro elevators to the east end tunnel portal, if the decision is made to not carry the CCT through the tunnel over the top of the Purple Line. The profile above shows the Purple Line with the CCT overhead. But if the CCT supporting structures are absent, the light-rail tracks can be shifted to be closer together and close to the south wall. A 6-8′ wide walking path could be on the north side. The walking path would only need to be several feet higher and separated from transit by a low fence in order to feel safe near transit, given the low speeds of the transit vehicles approaching the station platform.
Purple Line supporters should join trail users to advocate for this path, in the event the CCT is removed from the tunnel. This passageway would provide important pedestrian access between the Purple Line platform and the neighborhoods, businesses and schools east of Wisconsin Avenue. The Purple Line should carry the cost of building it since the Purple Line needs this access path.
3) Single-track Purple Line in the tunnel.
CCCT Chair Ron Tripp put the idea before the CCCT Board at the October board meeting that we should propose that the Purple Line be single-track in the Bethesda Tunnel. This would allow a full width CCT to share the tunnel with the Purple Line without any digging. I’m not a fan of this idea, but it does have enough merit to be taken seriously. The CCCT has not settled on its recommedations to address the Bethesda Tunnel cost issues yet, but single-track may be on the list.
Councilmember Berliner proposed a much longer single-track section for the Purple Line several years ago. His proposal was to single-track a 3500′ long section from the Bethesda Tunnel to the west side of the Columbia Country Club. The principal goal was to minimize the impacts on the trees and adjacent homeowners where the r.o.w. is only 66′ wide and where room to buffer the neighborhood is more limited than elsewhere on the r.o.w.
MTA studied Berliner’s single-track proposal and issued a MTA single track study (a pdf) with strong recommendations against the idea. MTA found that being able to operate only one vehicle between the Country Club and the Bethesda Station at a time would unacceptibly constrain the headway, to be at least 7 minutes. The minimum necessary headway needed to carry the heavy use in this section is believed to be 6 minutes or less. MTA was also concerned that since transit vehicles would have to leave the Bethesda station immediately, schedule problems that develop could not be corrected and would ripple through the whole system. MTA was also concerned that having only one track at Bethesda would prevent them from holding a back-up vehicle there to fill gaps in service. And finally MTA found that few trees would actually be saved during construction. Based on these findings, the County Council reluctantly dropped the idea.
The proposal to go to single-track only in the Bethesda Tunnel would result in an approx. 1500′ length of single-track, vs. the 3500′ length of Councilmember Berliner’s earlier proposal. I roughly guess that this shorter distance would take at least 1 minute off the time it would take a train to traverse the single-track section in each direction. That would mean a headway of less than 5 minutes might be possible – meeting the requirement for a 6 minute headway or shorter. That’s good. But I suspect the same issues about trains being required to leave the Bethesda Station immediately and not being able to store a back-up vehicle there would remain.
Single-track at a station, especially an end-of-line station, is a departure from what we usually see where single-track has been attempted. The parent of the Purple Line concept, the single-track Georgetown Branch Trolley, was actually planned to be double-track at all five stations along the line between Silver Spring and Bethesda, including at the Bethesda Station in the tunnel. The plan was to have trains pass at the station platforms. The stations were planned to be roughly equally spaced, at distances that would enable trains to pass at the stations and still maintain 6 minute headways. A key to making it all work was that the Georgetown Branch Trolley was to be a “closed” system that would never run on-street, so it would be possible to keep trains precisely spaced at about equal intervals. Keeping to carefully spaced intervals at all times is not considered to be feasible for the Purple Line because the Purple Line is an open system, that will run in streets and have traffic lights in parts of its route east of Silver Spring. These potential traffic interferences can introduce too much variation in train intervals for them to pass only at the stations without forcing trains to wait. Variation in train intervals is best corrected at the end-of-line stations, but the needed corrections may not be possible at a single-track end-of-line station.
Single tracking only at the Bethesda Station may be judged to create unacceptible problems for efficient transit operations. But this proposal to single-track a very short section has enough difference from Councilmember Berliner’s earlier proposal for a much longer section to merit a serious look from people who understand transit operations much better than I.
4) Safety of the Trail.
This is not a design idea, but an observation about irrational, and potentially damaging, assertions being made by some about safety of the trail in the tunnel.
Comments were heard during the Planning Board tour from the “Save the Trail” people that if the trail is elevated and placed in a confined space over the Purple Line, with no way to get off except at the ends, and without being able to see to the other end of the tunnel before entering, then the trail would be too dangerous and no one would want to use it. Ajay Bhatt, President of Friends of the Capital Crescent Trail, is quoted by Katherine Shaver in the Washington Post as saying:
“I can’t imagine people would enjoy that trail experience,” Bhatt said of an enclosed trail above trains, and “it seems like it will be a safety hazard” by attracting crime.
The problem with taking this position is that the existing trail looks like this now:
The trail we have in the tunnel now.
The existing trail is in a confined space, with no way to get off except at the ends, and without being able to see to the end of the tunnel before entering. So exactly how does Ajay Bhatt think that just elevating the trail by about 10′ will suddenly transform a trail he claims to badly want to save into a trail that is such a safety hazard that he cannot imagine anyone wanting to use it?
The danger in this “Save the Trail” position is that we are asking the Planning Board and County Council to spend many millions of dollars to keep the trail in the tunnel. If we raise groundless fears that a trail in the tunnel cannot be made safe and attractive, in a misplaced effort to make the Purple Line look bad, we seriously undercut our request to public officials to spend scarce money to keep the trail in the tunnel.
The second half of the Planning Board tour at Bethesda was along the proposed alternate street route for the CCT. Several ideas came up for discussion about how to put this route on steroids if the CCT is removed from the tunnel. But I’ve already written too much for one post, the alternate route will be the subject of a future post.