Editor’s note: The Thayer Avenue route discussed in this article is one of three proposed routes through Silver Spring. No route has been finalized as of this writing. (Mar 22, 2007)
A tunnel for the proposed Purple Line could be extended to avoid an elementary school footpath, state transit officials said.
The tunnel, part of a proposed Thayer Avenue route, would burrow beneath East Silver Spring Elementary School and a popular path off Thayer Avenue (above), engineer Joe Romanowski explained. He and other experts spoke with a neighborhood focus group Wednesday night at Oakview Elementary School.
“They were worried about kids crossing the light-rail tracks as it [the Purple Line] came out of the tunnel,” Mike Madden, of the state transit administration, told the group. “We’ve just extended that tunnel to go under that path.”
The Purple Line would then return to street level just west of the route’s intersection with Thayer Avenue. The tunnel could not be extended further east because of changes in elevation, Romanowski said.
Exactly how a tunnel would be constructed in that area is undecided. Engineers are drilling throughout Silver Spring to assess what lies beneath the street surface, consultant Joel Oppenheimer said. What they’ve found so far is a mixed bag.
“Some areas will have 40 feet of fill [soil], then good rock, then fractured rock,” Oppenheimer told the focus group. “It’s not going to be an easy place to tunnel.”
Two modes of tunnel construction have been proposed. With deep tunneling, machinery would drive through the bedrock without disrupting the street surface. However, engineers must determine whether deep tunneling can be done through Silver Spring’s calico subsurface, Romanowski said.
Tunneling also could be done by the cut-and-cover method. In that approach, the street surface is dug open so that a tunnel could be buried beneath the top soil. Robert Rosenberg, a resident who opposes this method, said it could impact about 60 privately owned lots between Silver Spring and Thayer avenues in East Silver Spring.
“They have no rights over backyard property,” Rosenberg told The Penguin. “We support some kind of deep tunneling through East Silver Spring.”
The costs of deep tunneling and cut-and-cover construction have not yet been compared, Madden, of the transit administration, said.
Image courtesy of the Maryland Transit Administration. Photo by Jennifer Deseo for The Silver Spring Penguin.
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I think this article incorrectly implies that one of the 3 major East Silver Spring alignments has been selected. The MTA is actually still studying options on all of the alignments. For example, discussion during last night’s meeting also introduced many refinements to the Wayne Avenue alignment as well.
Point taken, Robert. I’ll mention that at the top of my story.
Regarding the Wayne Avenue alignment, I’ll get to that after lunch. Must … eat!
[...] indicated that the state transit administration was leaning away from a subterranean route beneath Silver Spring and Thayer avenues in East Silver Spring. According to Ervin, the transit administration determined the cost of tunnel [...]