Erdman Anthony provided preliminary engineering, final design plan reviews,
and construction consultation services for the design/build replacement of dual
bridges, 383 feet and 480 feet in length, carrying I-81 over Stafford Meadow
Brook, a railroad, and an access road (SR 0081, Section 271) in Lackawanna
County. The project development included a 2-day VE/ACTT session in which final
bridge replacement scenarios were discussed among the project team, including a
number of contractors, to assist in the development conceptual traffic control
schemes and bridge types.
Traffic control was a critical issue, since the bridges are located near Exit
184, a high-traffic area providing access to the City of Scranton. Maintaining
four lanes of traffic required a three-phase construction scheme that first
temporarily widened the existing southbound bridge to accommodate four lanes
(Stage 1), then used crossovers to shift traffic onto the widened structure
while the northbound bridge was replaced (Stage 2). Traffic was then shifted to
the newly completed northbound structure while the existing southbound bridge
was removed and replaced (Stage 3). The design team studied crossover
alternatives that navigate a variety of obstacles on the bridge approaches,
including rock embankment in the median, lane bifurcation of up to eight feet,
and existing overhead sign structures. Other key design issues included
providing contractor access during construction (given the difficult terrain)
and optimizing bridge span arrangements and materials based on geological and
geographic considerations. The Erdman Anthony team used low-level aerial
photogrammetry with 3-D laser scanning to supplement conventional survey
methods, which were inhibited by the heavy traffic and steep terrain. In
addition, our team coordinated bridge design with the operations of the
Lackawanna County Rail Authority, the City of Scranton, and various review
agencies. The project required close coordination with the design/build team and
prompt review of contractor-prepared design plans.
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