I‐79 over North Boundary Road Design

In Cranberry Township, a dual three‐span concrete slab structure carries I‐79 northbound and southbound lanes over North Boundary Road. Due to the rapidly deteriorating condition of the bridges, District 10 of the Pennsylvania Department of Transportation (PennDOT) initiated a replacement project with an accelerated design schedule of ten months. To meet this demanding schedule, all work activities were conceptualized to occur within PennDOT’s existing right‐of‐way with no permanent right‐of‐way takes or temporary construction easements. Lochner led the roadway, traffic, and bridge design.

Lochner designed two new single‐span structures for I‐79 that maintain the existing horizontal alignment while raising the vertical alignment. This design allows for an increase in structure depth and provides the required minimum vertical clearance of 14 feet beneath the new bridges. Specifically, the new structures will consist of composite steel rolled beam superstructures with full‐height, pile‐supported abutments as integral abutments. Changes to the vertical and horizontal alignment of North Boundary Road were purposefully avoided to circumvent a recent township roundabout project adjacent to the site and to eliminate relocating several subsurface utilities, which could have potentially impacted the project schedule.

To mitigate poor soils within the project limits, extensive benching details were required in the median and along I‐79. The roadway was originally constructed of fill material primarily made of a loose‐to‐very‐dense gravel and sand mixture that overlaid bedrock. Due to an underlying layer of clay the project team encountered, Lochner recommended that 1.5 feet of undercut excavation be performed in areas where the existing concrete pavement would be removed. In areas of the temporary crossover, it was recommended that two feet of undercut excavation be performed. To limit the amount of undercut needed, Lochner eliminated constructing full depth pavement for the full limits of the roadway construction. Instead, full depth pavement will be constructed in areas where the existing concrete pavement is to be removed due to fill slope benching and structure abutment excavation limits. In areas where the existing concrete pavement will remain, a bituminous build‐up will be used to bring the roadway up to the proposed grade.

During a previous roadway paving project in the project area, only one lane of traffic was maintained in either direction and resulted in queuing on I‐79 as far south as the SR 228 interchange (approximately three miles south). Therefore, PennDOT required Lochner to design for two lanes of traffic in both the northbound and southbound directions during construction. Lochner’s design will move traffic through the work zone via a temporary bridge placed in the median between the dual bridges in conjunction with the construction of temporary crossovers to the north and south.

With a potential retail development west of the project and an established residential development and active township park to the east, coordination with Cranberry Township played a critical role in the project. Lochner helped to mitigate potential issues, such as short‐term detours for North Boundary Road during significant park events.

Lochner’s responsibilities also included performing an environmental assessment of the project area and preparing a National Pollutant Discharge Elimination System (NPDES), approval of which was obtained in just three months. The project team prepared a work zone analysis and incident management plan as well as coordinating with the local traffic incident management team on the relocation of the temporary median crossover and the on‐going installation of an intelligent transportation system along the I‐79 median.