McCormick Taylor was responsible for the design of the reconstructed roadway that raised it above the 100-year flood plain, and also a retaining wall that could withstand the fast-moving water of Gulph Creek during rain events.



Route 320 (South Gulph Road) was considered a “legacy” project by PennDOT District 6-0. Due to the complex nature of design, location, and permitting issues, this project faced many challenges during a nearly 20-year time period with several starts and stops before finally stalling. 


When McCormick Taylor was awarded the project, preliminary engineering had been started but was delayed trying to get environmental clearance. The team worked through the rigorous environmental process and was able to garner public support for the project. The design showed an elevated roadway out of the floodplain and a retaining wall also with a cantilevered roadway over the creek to avoid impacting the historic Hanging Rock.

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Existing condition


McCormick Taylor was able to complete preliminary engineering and final design in only three years. A retaining wall system (t-Wall) was designed to withstand flood waters of Gulph Creek. The mile-long roadway between Arden Road and South Gulph intersections consistently flooded during rain events and prevented access for emergency services throughout the area. McCormick Taylor worked through complex hydraulic models and found a solution to elevate the roadway out of the 100-year floodplain to keep it accessible to EMS. Another innovation was the design of a cantilevered roadway section. This piece extended one lane of roadway over the creek to avoid impacting the Hanging Rock. For a length of almost 1,000 feet this cantilever was utilized. The final piece of the puzzle was the intricate permitting process due to site location, restrictions, and the stream directly parallel to the roadway. The in-house environmental team was able to coordinate with all agencies and got a consensus that the project was satisfactorily designed and met all the requirements of the needed permit(s). With this consensus in hand, McCormick Taylor finalized the permitting process and was able to achieve the required permits on the first submission keeping the project on schedule.


Construction began in winter 2020 and the road was reopened in summer 2022. Improvements to the roadway include:

  • Realigned Route 320 (South Gulph Road) away from Hanging Rock, which had protruded into the roadway resulting in limited site distances,
  • Raised the profile of Route 320 (South Gulph Road) to meet the requirements for the 100-year flood elevation,
  • Reconstructed the cantilevered structure that carries Route 320 (South Gulph Road) over Gulph Creek,
  • Reconstructed the wall separating Route 320 (South Gulph Road) and Gulph Creek
  • Added a southbound right-turn lane at the intersection with Upper Gulph Road,
  • Installed ADA curb ramps and traffic signal upgrades,
  • And performed various drainage upgrades.

This project reinforces and improves PennDOT’s network and enhances safety on a heavily-traveled section of Route 320, while also preserving the historical importance of Hanging Rock.



2022 Project of the Year, ASHE Delaware Valley


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