The Silver Spring Penguin

The county’s planning department wants the state to look into a possible Purple Line tunnel through East Silver Spring, one transportation planner announced Monday night. (more…)

The Purple Line won’t roll down Sligo Avenue, but it could chug along Bonifant Street on its way to Long Branch, according to reps for the state transit administration.

At Monday night’s focus-group meeting in downtown Silver Spring, project manager Mike Madden said a route along Sligo Avenue was no longer under consideration. That alignment would have carried the light-rail line at street level between Long Branch and the Silver Spring Transit Center.

Impacts on the community, as well as the cost of tunneling beneath East Silver Spring to avoid those impacts, dictated the alignment’s elimination, Madden told The Penguin.

Instead, a street-level alignment could snake south from the transit center, then eastward on Bonifant Street. The alignment would turn north on Fenton Street, then eastward on Wayne Avenue. (See map above.)

However, tunneling beneath Bonifant Street won’t be possible, Madden said. From its elevated station at the transit center, the Purple Line would not have enough distance to transition into a tunnel, he explained.

Tunneling would be likely if a proposed east-west route between Thayer and Silver Spring avenues is selected, said Joe Romanowski, a consulting engineer for the state.

However, that alignment would not burrow beneath the proposed Studio Plaza development off Georgia Avenue, Madden said. Instead, it would run beneath Silver Spring Avenue, then turn north near Fenton Street. (See map above.)

Tunneling is also likely if a route is selected from Silver Spring Avenue near Georgia Avenue, directly to Wayne Avenue near Cedar Street. The tunnel would be deep enough so as not to disturb homes or trees on the street surface, Madden said.

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.