State transportation planners have added a third possible alignment to the list of routes under study for the proposed east-west transit line between Silver Spring and the Takoma/Langley Crossroads.

As part of the Bi-County Transitway, formerly known as the Purple Line, the proposed alignment would run along an existing storm sewer easement behind more than 50 homes on Silver Spring and Thayer avenues in residential east Silver Spring. The state is studying the area for a "cut-and-cover" section of underground light rail track.

According to a planning map from the Maryland Transportation Administration, the proposed transitway alignment would initially branch off Metro's Red Line in downtown Silver Spring, tunneling under Colonial Lane, crossing Georgia Avenue and moving east under Silver Spring Avenue. The tunnel shifts to the sewer easement between Silver Spring and Thayer avenues at Fenton Street.

The map shows the light-rail track surfacing on Thayer Avenue behind East Silver Spring Elementary School and connecting to Piney Branch Road, where it would continue on to the intersection of Flower Avenue.

Once built, the Bi-County Transitway will connect Bethesda and New Carrollton using either light rail or a type of dedicated bus lanes known as bus rapid transit. Planners had already identified two routes through east Silver Spring -- using either Wayne or Sligo avenues -- to get the transitway through the residential areas east of downtown.

The decision to add another alignment for a detailed study came in March as a result of public meetings held last fall with residents of Wayne and Sligo avenues, said Maryland Secretary of Transportation Robert L. Flanagan. Most of the residents along Wayne or Sligo avenues opposed having the transitway along their respective streets.

"The third alternative was developed in response to public comments," Flanagan said. "It's an iterative process whereby the MTA develops alternatives. The public gets to comment, we listen to that comment and then try to respond.

"In this case, the response was: There appears to be another alternative that could be developed."

Flanagan said the state also would study a no-build option for the transitway, as well as the option of upgrading existing bus service between Bethesda and New Carrollton.

During the next year, the state will study each of the selected routes to determine the feasibility of each, producing a draft environmental impact statement and selecting its preferred alignment. By spring 2007, the state is expected to decide which route and mode the Bi-County Transitway will take. The costs to build have not been determined.

Neighborhood residents living along Silver Spring and Thayer avenues learned of the addition of the third proposed alignment selected for further study during a community meeting in March, said Tim Haverland, a Silver Spring Avenue resident whose back yard includes the 25-feet-wide storm sewer easement.

The state would have to convert that right of way to a 65-feet-wide mass transit easement to put the light-rail tunnel through the nearly half-mile stretch of property between the two residential streets.

"Really, I think the thing that upsets us the most is the process," Haverland said. "This thing came late in the game -- March 15 -- and it's been very difficult to get information about this option. And very few of our public officials know about this."

Flanagan said the state has a federal responsibility to consider all feasible alternatives, which is why MTA added the Thayer Avenue route to its list of alignments for detailed study after Wayne and Sligo avenues were vetted publicly. "We will go to great lengths to work with all of the affected communities and get input, including constructive criticism, and just plain criticism, of all of our alternatives."

As to whether or not another east Silver Spring or Takoma Park street might appear on the state's list of proposed transitway alignments in the future, Flanagan said it is a nearly impossible question to answer.

"Any of the work and any of the studies that we're doing have to be understood in the light of the duty that the MTA has under federal law," he said.

As residents of Silver Spring and Thayer Avenues have garnered 140 signatures on a petition to remove their area from the transitway study, the neighborhood has been drawn closer, Haverland said. But the transitway project has the potential to do just the opposite.

"There are three alignments that have been proposed, all of which have some serious problems, I think, all that go through east Silver Spring," he said. "I think these three options have the potential to really drive a wedge, to pit neighbor against neighbor, and that's really unfortunate that that's happening."