Highway Under Hanging Rock In Upper Merion Reopens

KING OF PRUSSIA, PA — The construction project that caused the dreaded detour of the heavily traveled Route 320 that motorists driving to King of Prussia, who are unfamiliar with the windy back roads, land in Plymouth Meeting is finally over.

Route 320, also known South Gulph Road, reopened Thursday after PennDOT contractors completed a $9.2 million project.

It had been closed to motorists for nearly two and half years.

The state highway provides a direct route from Bala Cynwyd, Lower Merion Township, to King of Prussia, Upper Merion Township.

PennDOT contractors were tasked with realigning the roadway away from the historic Hanging Rock in the Gulph Mills village of Upper Merion Township.

The hanging rock, listed on the National Register of Historic Places, is a large natural rock that initially protruded 8 feet over the roadway at Gulph Mills. The size of the rock over the road, traveled by George Washington’s Army, decreased over the years due to accidents.

"This project reinforces and improves our network and enhances safety on a heavily-traveled section of Route 320 (South Gulph Road), while also preserving the historical importance of Hanging Rock," said Louis Belmonte, acting director of PennDOT’s district 6.

Route 320 had been closed to through traffic between Upper Gulph Road and Arden Road since construction began in January 2020.

Allan Myers, LP of Worcester, Montgomery County was the general contractor on the project, which was financed with 100% state funds.

Under the project, PennDOT's contractor:

• Realigned Route 320 away from Hanging Rock, which had protruded into the roadway resulting in limited site distances;
• Raised the profile of Route 320 to meet the requirements for the 100-year flood elevation;
• Reconstructed the cantilevered structure that carries Route 320 over Gulph Creek;
• Reconstructed the wall separating Route 320 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.

Information about infrastructure in District 6, including completed work and significant projects, is available at www.penndot.pa.gov/D6Results. Find PennDOT's planned and active construction projects at www.projects.penndot.gov.