This is a multi-phase project to reconstruct approximately two miles of I-476, the four-lane Northeast Extension of the Pennsylvania Turnpike and to replace two major bridges. Roadway design constraints included relocating the roadway on a new alignment, maintaining two lanes of traffic in each direction during construction and widening the median and shoulders in the final condition. Innovative solutions were required to meet the project constraints and minimize impacts due to the mountainous topography of the site.

Modjeski and Masters performed an alternatives analysis during the preliminary design phase. Thirteen alternative alignments were initially studied, followed by a detailed investigation of three alternatives. An alignment alternative relocated west of the existing roadway was selected for this project based on issues relating to design, future widening, staging, constructability, environment and cost.

In addition a comprehensive study was performed to evaluate replacement of the existing bridges. The preliminary design also included preparation of the TS&L, Design Field View Report, Line and Grade Report, Preliminary Right-of-Way Plans and a Categorical Exclusion Evaluation.

The second phase of the project was for Final Design of the contract plans and documents. The final plans included the final Roadway and Right-of-Ways plans, a detailed four stage traffic control plan in addition to an extensive Erosion and Sedimentation Control Plan, Post Construction Stormwater Management Plan, Wetland Mitigation Plan in addition to a Joint Permit Application.

The proposed replacement bridges included dual, 6-span steel girder bridges over the Lehigh River for a length of 1,585 feet and 1,530 feet. The Pohopoco Creek replacement structures were comprised of dual 4-span steel girder bridges each with a total length of 1,020 feet.

Also, the site topography necessitated a 1,900 foot soil nailed retaining wall near the southern end of the project and an 800 foot precast concrete T-wall at the north end. A concrete box culvert extension was also required in addition to a precast concrete arch culvert under a relocated hiking trail.