Wednesday, June 28, 2006

The Tunnel That Was to be

District Office of Planning and U.S. National Capital Planning Commission

The idea of incorporating the excavation of the existing underpass within a 3 lane per direction cut and cover tunnel directly beneath the SCS row was included in planning in 2002-2003, along with the options of parallel alignments to the east, but not the west to minimize impacts on existing residential neighborhoods.

This tunnel was to extend initially north to I Street to meet the existing connections to the SW/SE/Center Leg Freeway, with design flexibility to for the latters’ underground replacement.

However, to its south, this tunnel would not have the option of surfacing onto the new bridge, but rather commit itself to the more ambitious and more expensive option of continuing it south beneath the Anacostia River to I-295 and the Suitland Parkway, with three lanes per direction.

In 2003, US NCPC and the DCDOP/DOT agreed that such a tunnel was vital for regional transportation and for a more pedestrian friendly South Capitol Street corridor. Their studies for the South Capitol Street corridor included this 6 lane cut and cover tunnel as a given with all three of the surface options then under formal consideration: namely, what was essentially the eastern half of the South Capitol Mall concept from Extending the Legacy, a 195 foot wide linear park; a narrower but symmetrical 100 foot median green way; and a third option to maintain the existing 130 foot right of way.

According to the January 2003 NCPC South Capitol Street Urban Design Study Chan Krieger & Associates Architecture & Urban Design, with Economic Research Associates (ERA) Economics Development

The best opportunity to redirect regional traffic lies with the long term redevelopment of the South Capitol Street corridor, which deserves to become a beautiful, ceremonial, vibrant, and mixed-use southern gateway to the Capitol. This transformation can be achieved only if much of the regional traffic that the corridor currently caries is redirected to a high-speed tunnel. Such a tunnel would more directly connect the Anacostia Freeway (I-295) and the Southwest Freeway (I-395). Regional traffic would travel from Anacostia Freeway under the River in the new tunnel, below South Capitol Street to I-395 at the Southwest Freeway. The Suitland Parkway approach to Washington would maintain its parkway quality, cross a new bridge at the Anacostia River and move along a more boulevard-like South Capitol Street, lined with a mix of office, retail, and residential uses.

A tunneled interstate connection along the South Capitol Street alignment will allow for traffic reduction at all river crossings and lead to lower vehicular speeds, wider sidewalks, added cycling lanes, and safer pedestrian crossings. Great boulevards such as Pennsylvania Avenue could thus be restored to provide retail shops and services for neighborhoods, and sites for new national monuments. (at page 41)
According to the November 2003 District Office of Planning South Capitol Street Gateway and Improvement Study
A tunnel under the South Capitol Street corridor would provide a new link in the transportation network with many benefits. Much of the traffic now on South Capitol Street consists of trips through the corridor, not to it. A tunnel between I-295 east of the Anacostia River and the existing I-395 Third Street tunnel would carry trips bound for downtown Washington and beyond, removing the traffic from the surface streets. Constructing a tunnel to carry through traffic will alleviate congestion on South Capitol Street. This will be essential for South Capitol Street's transmogrification into the centerpiece of a pleasant and livable neighborhood. The tunnel would alleviate the burden of commuter traffic on the entire street network. Including a tunnel in the study area's improvements is the only scenario that permits the added benefit of removing the Southeast Freeway. The tunnel portals are a critical part of the study area's urban design considerations and can be configured in many different ways. East of the river, their design must respect the Popular Point parkland and Anacostia's historic neighborhoods. The north end of the tunnel, which connects to I-395 and the center leg tunnel, should be linked with the existing inter stare system without adversely impacting the area southwest of the U.S. Capitol grounds. (at page 74, section V Creating a Monumental Gateway-pdf)

Oddly, though this tunnel would connect two existing interstate highways, the cross section shown would be substandard to U.S. Interstate highway design by not indicating sufficent width for shoulders, even though there's sufficent space for such a cut and cover tunnel within the existing 130 foot right of way.

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