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These modular systems allow rapid design and
construction while maintaining the flexibility to fit a wide range of
sites. Three-sided structures are frequently used for highway, airport,
railroad, park, wetland, environmental applications, and more.
Increasingly, multi-disciplinary teams including engineers, architects,
planners, and concerned neighbors are tailoring these efficient small
bridge systems into structures that provide much more than utilitarian
functions. What is CSD?
According to the Federal Highway Administration,
Context Sensitive Design is a collaborative, interdisciplinary approach
that engages all stakeholders in the development of a transportation
facility that fits its physical setting and preserves scenic, aesthetic,
historic, and environmental resources while maintaining safety and
mobility. Stakeholders typically include local public and quasi-public
agencies, environmental groups, community and civic groups, and
concerned neighbors. Engineers, architects, and planners often
facilitate the discussion by providing technical input and details on
potential options.
The process begins with the first public
outreach meeting which introduces the project and the goals for
subsequent meetings. The number of meetings needed varies with the scope
and complexity of each project as well as the interest level of the
group. Engineers typically describe the constraints of the site and
design challenges. Research on similar example projects is a valuable
tool for explaining options for the site and advantages of each option.
Today many engineers and architects have access to photograph
manipulation software, which allows them to create project simulations
or renderings based on photographs of the existing site. Renderings are
very powerful tools for explaining how a structure will work, look, and
fit with the surroundings. Several options can easily be seen and
understood by all stakeholders. These renderings can be updated and
become more realistic as the process approaches a final structure type
selection. Architectural details such as landscaping, finishes, colors,
and other features are easily incorporated and modified as the group
investigates new options. A key to the success of this process is an
experienced and knowledgeable facilitator who can keep meetings
productive, allow all stakeholders an equal voice, and guide the group
to an effective, workable solution.
Community values obviously vary for each
project, but the goal of context sensitive design is always for
stakeholders to reach a consensus on the overall project direction.
This consensus yields benefits for all involved.
Stakeholders feel a sense of ownership in the project that can minimize
the resistance that naturally occurs due to change in a neighbor’s back
yard. The community is more supportive of local governments,
transportation officials, and contractors when they feel a sense of
ownership in the project. Temporary inconveniences become more tolerable
when neighbors recognize that the new structure will be responsive to
their specific concerns and wishes. |
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We will examine two very different bridge projects
where precast three-sided structures brought modern construction techniques,
materials, engineering methods, and safety regulations to historical and
scenic sites. In each case, the new structure economically maintained the
historical and aesthetic significance of the site and ensured decades of
safe operation with minimal or no maintenance.
Coton Bridge
The entrance to a new Lansdowne on the Potomac
residential development in northern Virginia needed to cross Goose Creek,
one of the state’s designated scenic rivers with a world-class reputation
for pristine waters. A popular destination for canoeing and fishing, the
stream also runs through an area rich in historical significance. The Goose
Creek Scenic Advisory Board which is appointed by the state to monitor and
maintain the environmental, historical and aesthetic standards of the area,
played a key role in selecting a structure. A series of meetings was held to
ensure that the new bridge would honor the past and maintain the
environmental standards and aesthetic concerns of the community.
Attempting to resemble other historic structures in
the area, members of the advisory board requested the traditional look of
stone. BridgeTek, LLC, the local provider of CON/SPAN Bridge Systems worked
with engineers from Urban Engineering and Associates, Inc. and architects
from Lewis Scully Gionet Landscape Architects to create a photographic
simulation of the developer’s vision for the bridge. A nine-cell precast
structure with a custom stone form liner finish and an arch shape similar to
other historic structures in the area was presented. This helped the group
visualize the structure and eventually choose the arch-box concrete
structure instead of a more conventional steel girder bridge. The advisory
board’s chairperson, Helen Casey, was immediately drawn to the look of the
multiple-cell arch option. “When they put this up on the screen in a
computer-generated version, I was stunned,” she said. “I said, ‘I can’t find
anything wrong with it.’”
The structure met the aesthetic and historic
requirements of the site but also offered environmental advantages. Over
4,865 tons of concrete was poured at the precast plant rather than in the
sensitive Goose Creek valley. The contractor, Westlind Construction, was
also able to bury utilities in the 5 feet of fill over the structure. This
prevented a considerable amount of excavation in the channel and resulted in
a significant cost savings as well.
Lansdowne Development Company privately funded this
structure and the Virginia Department of Transportation took over ownership
and maintenance responsibilities after construction. The developer was
initially interested in stone facing over the precast structure, but VDOT
preferred a form liner finish to minimize future maintenance. The form liner
provider, Architectural Polymers, created custom form liners using stones
from old locks in a nearby historical canal as a template. Each individual
stone was stained after construction to more closely simulate a stone wall.
The bridge was designed to last 100 years with minimal maintenance.
The 446-foot-long by 82-foot-wide structure was
named Coton Bridge to commemorate the 18th-century Coton Plantation, which
had been located in the area and is now part of the new development. In his
remarks at the ribbon cutting ceremony, Virginia Governor Mark R. Warner
stated, “We’ve taken this wonderful setting at Goose Creek and created a
piece of history... people will look back over the next 100 years and say
‘what a beautifully constructed bridge.’” This would not have been possible
without the contributions of all stakeholders.
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Use of a buried bridge
allowed utilities to run through the fill over the structure
rather than disturbing the stream and running pipes through the
channel. In addition, this bridge has no deck to maintain. |
Animal Bridge
Chicago’s reconstruction of more than 6 miles of
South Lake Shore Drive improved access to lakefront recreation and tourist
attractions by including five three-sided structures. Among these was one of
Chicago’s most unusual and historic bridges. The Animal Bridge carries South
Lake Shore Drive over a lagoon to historic Jackson Park. The park was
originally envisioned in 1871 by Frederick Law Olmsted, the famed designer
of Central Park in New York City as well as many other green spaces
throughout the country. Construction of this bridge was delayed until 1903
when German architect Peter J. Weber won a design competition. Reflecting
the wind and water theme Olmstead had envisioned for Chicago’s southern
parks, his concept included sculptured rhinoceros and hippopotamus heads,
water deities and a ship’s prow. Construction was finished in 1904 using
pink St. Cloud granite and sandstone from the Kettle River Quarry Company of
Minneapolis.
Planning for the South Lake Shore Drive improvements
started in 1998. The city invited the participation of many community
organizations including the Lake Michigan Federation, Friends of the Parks,
the Jackson Park Advocacy Council, and the Lake Shore Drive Advisory Group.
Consoer Townsend Envirodyne Engineers, Inc. provided engineering and
architectural services. Extensive research on the history and construction
of the park and bridge was performed for Level-I Historic American
Engineering Record documentation. The group decided that the bridge should
be reconstructed, so work soon began on specifications and drawings for the
disassembly, restoration, and reconstruction of the stone facing.
The original concept called for a 15-foot-wide
pedestrian tunnel between the Animal Bridge and a nearby intersection.
“Community members wanted a wider and more open pedestrian tunnel leading to
the lake front area,” according to Dipal Vimawala from CTE Engineers. In
response, engineers moved the bridge 20 feet north and called for channel
realignment to accommodate a 36-foot-span adjacent pedestrian structure.
Additional design challenges were soon apparent. The
Chicago Department of Transportation required phased demolition and
construction to keep traffic moving on the busy South Lake Shore Drive.
Construction was also constricted to winter months so that boat traffic
under the structure was not disrupted. The bridge needed to be widened,
realigned, and moved from its original location to accommodate safer traffic
lanes and pathways for pedestrians and bicyclists. The structure was also
moved from its original location in order to improve traffic flow into a
nearby intersection. Survey requirements were developed to ensure that the
new structure would have the exact geometry of the existing structure.
Methods were specified to attach the original stone facing to a new
structure. The new structure also allowed for modifications that would
accommodate the heavy pedestrian, bicycle, boat, and highway traffic that is
signature of this busy park.
Many of these design challenges were resolved when a
46-foot span by 11-foot, 5-inch rise three-sided structure manufactured by
Egyptian Concrete of Salem, Illinois was chosen. The shape of the new
structure was an exact match with the existing structure, and the precast
pieces could be produced off site, reducing construction time compared to a
cast-in-place solution. Each piece of the original stone façade was mapped,
catalogued, and removed. The stone pieces were then cleaned, refurbished,
and some even reconstructed due to irreparable damage. Precast bridge units
were delivered to the site and placed on 20-foot-tall cast-in-place
abutments by Walsh Construction Company. The new structure was 105-feet long
and placed 20 feet away from the original location. After the precast
structure was in place, the refurbished façade pieces were placed to finish
the bridge.
Reconstruction of the Animal Bridge at Jackson Park
satisfied all six goals of CSD. The scenic, aesthetic, and historic
qualities of the site were maintained and enhanced. A new bridge alignment
with a nearby intersection and widened roadway improved the safety of
drivers in the area. Mobility for pedestrians, bicyclists, boats, and
vehicles was also improved. In addition, public inconvenience was minimized
using precast concrete elements and phased construction. With construction
primarily in the winter months, the new structure was complete for the start
of boating season. Thanks in part to CSD, this bridge will exist for
another hundred years as a landmark in the famous south Chicago green space.
Consider the context
These are just two of the many examples where
stakeholders of small bridge projects have chosen three-sided structures as
the most effective option. Integrating modern engineering and construction
techniques with open communication and collaboration which are the heart of
the CSD method enhances our communities. |
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CSD Resources
Several publications can provide more information.
Flexibility in Highway Design (FHWA
Pub. No. FHWA-PD-97-062) is an FHWA publication about designing highways
that incorporate community values and are safe, efficient, effective
mechanisms for the movement of people and goods.
Building Projects that Build Better
Communities — Recommended Best Practices, Washington State Department of
Transportation, 2003. In this publication you will find information
on using the community partnership approach, setting the stage for success,
working through design, review and approval, building your project,
evaluating, adjusting, and improving, case studies from WSDOT/Local Agency
partnerships in Community-based Transportation Design.
International Scanning Tour on Highway
Geometric Design Practices for European Roads — Mobility, Safety, Community
Issues, Context Sensitive Design (FHWA Pub. No. FHWA-PL-01-026). The
objective of this scanning tour in June, 2000 was to review and document
procedures and practices in highway geometric design and context sensitive
design in several European countries.
Getting It Right in the Right-of-Way: Citizen
Participation in Context-Sensitive Highway Design by Deborah L.
Myerson. This is an action guide for people who want roads that preserve the
beauty of their communities, as well as roads that are safe, durable, and
economical to maintain. The guide includes sample state legislation that
citizens can use to advocate for context-sensitive design through their
state legislatures.
You can also find help on the Web.
Pilot state DOT sites provide data, too.
Connecticut:
www.fhwa.dot.gov/csd/conn.htm
Kentucky:
www.fhwa.dot.gov/csd/kty.htm
Maryland:
www.fhwa.dot.gov/csd/mar.htm
Minnesota:
www.fhwa.dot.gov/csd/minn.htm
Utah:
www.fhwa.dot.gov/csd/uta.htm
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