Drawing Bridges - Pushing the Limits: New Adventures in Engineering - page 53

I-95 through Washington proper, and that leg of the interstate system was permanently redirected
to its present route along the I-495 Capital Beltway, which includes the Wilson bridge. By the late
1970s, when structural deficiencies in the bridge were identified, a major rehabilitation project was
begun, with much of the deck-replacement work taking place between 10:00 p.m. and 5:00 a.m.
so that the full six lanes of the bridge could remain open during most of the peak traffic hours and
accommodate the 108,000 vehicles that were then using the span each day.
A major study was initiated in the late 1980s to consider replacing the bridge and reconstructing
the roads in its vicinity, and a concept competition was held to find innovative solutions to the prob-
lem. The consensus solution, a fourteen-lane bridge to the south of the present Wilson bridge, was
not found fully acceptable by a jury of experts, but an environmental-impact study of the inevitable
project was carried forward nonetheless. By the early 1990s, traffic volume on the bridge was more
than double what it was designed to carry, and in 1992 a coordination committee representing those
most affected by the project was appointed by the Federal Highway Administration to oversee a
new improvement study for traffic problems in the area. Specifically, the committee was charged
with identifying a “solution which enhances mobility while assuring that community and environ-
mental concerns are addressed.” Among the outcomes of the study was the finding by a bridge-in-
spection firm that the useful life of the Wilson bridge would be reached in 2004, a limit determined
principally by the accelerated deterioration taking place under increased truck traffic, amounting to
about 17,500 trucks per day carrying 1.3 percent of the total volume of all U.S. truck shipments by
manufacturers, wholesalers, and others.
Among the options considered for improving the flow of traffic was to build a new span ten miles
downstream. However, since 85 percent of the traffic over the existing bridge has its origin or des-
tination within the Washington metropolitan area, it was estimated that the new bridge would reduce
traffic across the present span by only 10 percent. The problem of replacing Wilson bridge with a
larger-capacity span at the same location also involved redesigning nearby highway interchanges,
which were overburdened as well. Such redesign and construction would have obvious impacts on
the local community. Public meetings and citizen workshops provided opportunities for input from
interested groups.
In 1996, the coordination committee, comprising transportation and elected officials from the af-
fected area, decided upon a preferred conceptual design for a replacement bridge: a pair of six-lane
spans, the exact nature of which would be determined via a design competition. While such a com-
petition might account for only 10 percent of the total final design effort, it would provide a basis
into which to incorporate subsequent refinements and the many detailed design decisions that go
into such a project.
Although an unusual means of selecting a bridge design in the United States, design competitions
have a long and rich tradition elsewhere in the world, especially in Europe. In the case of procuring
a design for the replacement of Wilson bridge, the method was chosen at least in part because of a
highly successful application of the design-competition concept about a decade earlier to replace a
state-highway bridge in the historically sensitive region of Annapolis, Maryland.
In the late 1980s, the sixty-year-old drawbridge carrying Maryland Route 450 over the Severn
River at the state capital was badly in need of replacement. The bridge site is at the eastern gateway