Wednesday, June 28, 2006

Recycling the existing underpass
within a longer cut and cover box tunnel

The existing underpass with it 2 lanes in each direction occupies less then half of the existing 130 foot lateral space between the buildings facing South Capitol Street, and is very little longer then that required to cross beneath M Street. This provides little space to widen the M Street overpass, e.g. it is unlike the open depressed northern Connecticut Avenue approach to DuPont Circle or portions of New York Avenue, hence this existing structure provides little opportunity to deck over the existing approaches that surface at N and O Street.

If the idea is to delete the open approaches for a more dignified setting for St. Vincents Church, and to confine construction to existing right of ways, deconstruct the transitions and incorporate the existing excavation into a larger cut and cover tunnel.

With outer and center tunnel walls each 4’ wide accommodating twin tunnel ways, the existing 130’ building line to building line right of way could provide 3 continuous lanes per direction flanked by 12’ and 10’ shoulders ( 4/12/36/10 /4/10/36/12/4= 128’)

To connect with an evolving road network, it would surface at its north at I Street to meet the existing connections to the SW/SW/Center Leg Freeway; and ultimately the latters’ underground replacement. To the south it would surface in the vicinity of Potomac Avenue, directing to the replacement South Capitol Street Frederick Douglass Bridge. This would include the concurrent or latter addition of a tunnel continuation southwards beneath the Anacostia River to connect with I-295 and the Suitland Parkway.

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