City planners have proposed constructing a $1 billion tunnel beneath the Anacostia River as part of efforts aimed at revamping the South Capitol Street corridor, according to a study released Thursday.

The report, which envisages a return to South Capitol Street’s earlier centrality as a key axis of the original L’Enfant City, also endorses the removal of the “jumble of elevated highway infrastructure” represented by the Southeast Freeway.

The tunnel, linking I-295 and the Suitland Parkway to I-395 and the Third Street Tunnel, would siphon off traffic at the Southeast-Southwest and Center-Leg freeways’ South Capitol Street interchanges, thereby “diminish[ing] the amount of volume you have on the neighborhood streets,” said District Department of Transportation Director Dan Tangherlini.

During a ceremony marking the report’s release last week, D.C. Mayor Anthony Williams (D) called South Capitol Street’s rehabilitation “integral” to the Anacostia Waterfront Initiative — an ambitious project to revitalize the nine-mile stretch from the Tidal Basin to Maryland. Given South Capitol’s importance as a point of entrance for visiting dignitaries arriving from Andrews Air Force Base, Williams also praised the plan as vital to burnishing the city’s image.

Anchoring the South Capitol corridor to the broader Anacostia waterfront neighborhood would be a new, aesthetically pleasing Frederick Douglass Memorial Bridge — built to allow pedestrian and bicyclist access to the water, as well as a transit line — and patterned after the example of the Memorial Bridge, whose close-to-the-water construction allows it a more seamless meeting with the river’s shoreline.

“If we can reduce the impact of the traffic and reduce the scale of the bridge so that you actually draw people across it … we think that what you’ll have is an enhanced vibrancy in the communities in the east and a rebirth in the communities in the west,” Tangherlini said.

The current Douglass bridge, dating to 1949, is deteriorating and in need of replacement, he said.

The comprehensive plan envisions South Capitol as an at-grade, 130-foot-wide, six-lane, “grand and ceremonial street” — with a median and broad, tree-shaded sidewalks — tied to the city’s monumental core.

As part of this vision, tree-lined roundabouts could be placed at South Capitol’s intersection with Virginia Avenue, as well as at Potomac Avenue, the report said.

In addition to reconfiguring many of the corridor’s thoroughfares, the proposal suggests introducing light rail or other rail transit along the gateway, such as at Half Street Southeast.

Officials hope improvements to the physical transportation infrastructure of the area will promote mixed-use development and cultural regeneration throughout the surrounding neighborhood.

“South Capitol is not really a commercial street. It’s like a highway,” said D.C. City Councilwoman Sharon Ambrose (D-Ward 6). But if it were to become a major boulevard, “can’t you just see lovely little restaurants with outside tables and people being able to sit outside and look straight down the street to the Capitol?” she enthused.

The estimated cost of the project, which does not include the creation of a new transit line, is more than $1.5 billion.

DDOT has requested $61 million in this year’s federal highway bill to stabilize the current Frederick Douglass Memorial Bridge, in order to “buy” time to undertake an environmental impact analysis and other preliminary design and engineering work, said Tangherlini.

The roughly $1.5 billion needed to carry out the project in its entirety would come in large part from the subsequent highway reauthorization slated for 2009, Tangherlini added. Completion of the South Capitol Street Gateway project is not anticipated before 2015.

“It’s going to cost money. It is not for free,” asserted Rep. Steny Hoyer (D-Md.), who spearheaded the drive to secure the $500,000 needed for the study in fiscal 2002. “I will be there every step of the way trying to get all of the resources we need to effect the completion of this vision.”

The draft South Capitol Gateway and Corridor Improvement Study — conducted by DDOT in conjunction with the U.S. Department of Transportation, the National Park Service and in consultation with other federal, state and city agencies — is open for public comment until July 3. It will be forwarded to Transportation Secretary Norman Mineta and submitted to Congress this September. To view the draft proposal, go to www.publicspace.justicesustainability.com/southcapitol/index.shtml.