Fifty years ago, S.R. 309, which runs through the heavily developed suburban Montgomery County, Pa., represented the state of the art in highway construction. By the time planning and reconstruction started in 1993, it was in danger of being left behind, like the former shell-home of a hermit crab, discarded on the beach. More than 65,000 vehicles a day now travel on S.R. 309. Traffic has grown prodigiously since the highway was first constructed, and design standards have grown, too.
S.R. 309 was suffering from short acceleration and deceleration lanes, a lack of shoulders and a narrow median. The entrance and exit ramps were the scene of frequent rashes. At the Fort Washington Interchange with the Pennsylvania Turnpike, the highway subjected motorists to inadequately long acceleration and deceleration lanes, inadequate weave areas between the loop ramps of the cloverleafs and tight, substandard radii on all the ramps. Commuters suffered through daily traffic backups at the nearby Pennsylvania Turnpike toll plaza.
Something had to be done.
So the Pennsylvania Department of Transportation (PennDOT) commissioned Gannett Fleming to perform preliminary engineering and environmental studies for reconstructing 10 miles of Rte. 309 as a limited-access expressway. The conceived project included rehabilitation of eight interchanges, redesign of two interchanges, replacement of eight overhead bridges, widening and rehabilitation of 16 bridges and design of 30,000 ft of retaining walls. Gannett Fleming also prepared a categorial exclusion evaluation, which included noise studies and an evaluation of how the project would affect archaeological, cultural and historic resources; wetlands; threatened and endangered species; public parklands; and Section 4(f) resources.
Widening Rte. 309 meant widening several bridges over Rte. 309, including the six-lane Pennsylvania Turnpike bridge from 140 ft long to 280 ft long. Somehow, traffic on all six turnpike lanes was maintained during construction.
At the Fort Washington interchange, they constructed a flyover ramp to carry southbound Rte. 309 traffic onto the turnpike.
All ramps were kept open at the Fort Washington interchange during construction.
To offset unavoidable wetland damage, Gannett Fleming designed a 2,600-ft-long wetland and stream mitigation corridor, consisting of wetland creation, wetland enhancement, stream enhancement and easement sites.
Nearly 10,000 ft of new sound wall was constructed along the highway to minimize noise from the highway in the community.
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