I) In the event of the adaptation of a full river tunnel crossing, as proposed by the Symonds Engineering Group and the Alexandria based All Tunnel Alliance, such a tunnel plan should be built with the Alexandria Orb interchange with several fewer ramps, with I-495 fully covered from the Orb eastwards. As shown in the Potomac Rossing Consultants, this portion of I-495 in the vicinity of Hunting Towers is apparently shown as an uncovered trench roadway. This treatment would replace the raised abutment area of a bridge with a deck that would slope downwards from Washington Street to Royal Street.
II) In the event of a bridge, whether the official configuration officially selected in September 1996, or a variant of the 10 lane bridge proposed by the Alexandria group Coalition for a Sensible Bridge, with or without a railway in the median that would drop below the I-495 roadways which would converge to thread the needle between the northernmost Hunting Tower and St. Mary's Cemetery, adopt some sort of modest cantilever to be built together with vertical sound walls along the sides of the bridge as it passes through Jones Point Park. The EIS already recommends vertical sound walls for this area which would be 17 feet in height.
A cantilever lip over the edges of the highway would have several intrinsic benefits:
a) noise retention
b) vehicular traffic emissions control
c) relatively low cost, given the inclusion of the above mentioned 17 foot high vertical sound walls. By there very nature, this cantilever could be added at a later date, as part of a general long range plan to provide a variety of transportation alternatives along the Wilson Bridge replacement. Yet, having these cantilever lip precast and integrated
with the vertical sound walls may well lower the ultimate construction costs.
d) relatively little change in the bridge's profile, given the inclusion of the 17 foot high vertical sound walls scheduled for this segment of I-495.
The additional potential benefits of a cantilever lip are the development of a system of bicycle/pedestrian pathways along/atop the edges of I-495; these would extend directly from the outer edges of the eastern portal of the covered area of the Washington Street Urban Deck, along either or both sides of I-495 eastwards to the edge of the Potomac River at the eastern edge of Jones Point Park, where they would end, where they would be connected by a brief deceiver of I-495, similar to as officially proposed on Rosalie Park, for a pedestrian platform providing a magnificent river's edge vista to both the north and the south right at this Virginia gateway. The fact that this is the gateway to Virginia, and that this project's final record of decision is being made at the start of a new millennium would conspire in favor of the extra costs.
This potential pathway system system could be used either to replace or supplement the officially proposed bicycle/pedestrian path that is already to be included in any bridge constructed here. Employing them as a replacement would result in a somewhat steeper grade for the abutment area than a path design from the Washington Street Urban Deck to the I-495 roadway elevation, making them more appropriate as a supplemental system that could be added at relatively low cost if cast integral with the sound walls, if not something added later.
In any instance, the bridge design should include the necessary structural strength along its outer edges to ultimately support this inclusion.
III) Bridge structure should be constructed with highest regard to noise. Additionally, the undersides should be attractively finished (as it apparently appears in the formal renderings on the official Wilson Bridge web site at ww.wilsonbridge.com The fact that the newer bridge will have far, fewer "piers" (indeed it will not have piers as this term usually suggests, but rather an attractive arch like design), makes possible a far nicer area under the bridge qualitatively, although quantitatively, more of Jones Point Park would be under the bridge.
Douglas A. Willinger
Takoma Park Highway Design Studio