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Squirrel Hill Tunnel Rehabilitation

Tunnel rehabilitation transforms outdated infrastructure into modern mobility innovation.

  • Squirrel Hill Tunnel Rehabilitation-Gannett Fleming

    View from edge of suspended slab at the open tunnel cross section.

  • Deteriorating tunnel ceiling: View of dark, deteriorating tunnel ceiling-Gannett Fleming

    A dark, deteriorating tunnel ceiling created safety hazards and caused drivers to slow down when entering.

  • Slab Rehabilitation: Crews working to repair a severely deteriorated slab-Gannett Fleming

    Crews repair a severely deteriorated slab that serves as a roadway for motorists and a ceiling for the basement beneath it.

  • Steel Struts: View of tunnel ceiling and the steel struts-Gannett Fleming

    Steel struts support the concrete against the lateral earth pressure on the tunnel.

  • Portal Building: Exterior view of Squirrel Hill Tunnel-Gannett Fleming

    The tunnel is flanked by portal buildings on each end, which serve as control centers for the tunnel's various systems.

  • New Conduit: Close up view of circuit-Gannett Fleming

    The project included 926,000 linear feet of circuit, which equals 175 miles.

Pennsylvania Department of Transportation District 11-0

Pittsburgh, Pennsylvania

Our Role
Final Design, Tunnel Inspection, Evaluation, and Repair, Structural, Mechanical, Electrical, Lighting.

4,225 feet
Construction Cost
$49.5 million
5 years
  • Provided plans, specifications, and estimates (PS&E) package for PennDOT to use for bid solicitation
  • Updated tunnel life safety, ventilation, and lighting systems
  • Repaired the East and West Portal Buildings
  • Modernized tunnel systems to meet current code requirements.

Completed in 1953, the Squirrel Hill Tunnel provides a crucial link between Pittsburgh, Pennsylvania, and the city’s eastern suburbs. As business and industry grew in the mid-20th Century, construction of the tunnel helped the city handle traffic from the east.

The average daily traffic (ADT) travelling through the tunnel has increased to more than 100,000 vehicles. Although the 4,225-foot tunnel has held up well, PennDOT determined that many of the structural, electrical, ventilation, control, and fire and life safety systems were in need of repair or replacement. In addition, by improving the interior lighting and removing the ceiling, the rehabilitation could help to negate a visual effect that had drivers braking as they approached the tunnel.

What We Did

In 2010, PennDOT hired Gannett Fleming to prepare rehabilitation contract documents for this 60-year-old tunnel. The resulting design modernized the existing tunnel systems to meet current American Association of State Highway and Transportation Officials (AASHTO) and National Fire Protection Association, (NFPA) 502 “Standard for Road Tunnels, Bridges, and Other Limited Access Highways” standards. The project included full retrofit of multiple tunnel structural systems, upgrade of the fire life safety system, rehabilitation of the ventilation system, full replacement of the electrical and lighting systems, and other specialized upgrades.

One of the most creative aspects of the project involved removing the existing tunnel ceiling inside the small window of weekend closures. This increased the vertical clearance, reduced the number of delays caused by over height trucks, and improved lighting to allow motorists to maintain highway speed through the tunnels. A safer environment for the travelling public was provided with the installation of new monitoring systems and oil/water separators and safety improvements by upgrading the fire suppression and life safety systems. All of the improvements added approximately 50 years to the useful life of this critical piece of infrastructure and improved the travel experience for more than 100,000 motorists that use the tunnel to commute between Pittsburgh and suburbs east of the city each day.

Key Features

  • Balanced the multiple and varying design criteria that governed the transportation, structural, electrical, mechanical, fire life safety, and environmental aspects of the projects
  • The project employed nearly a dozen design codes, forcing the design team to make many decisions to adhere to the most stringent guidelines
  • Removed nearly 18,000 square feet of tunnel ceilings, providing a higher vertical clearance and a less restricted feel, as well as improved emergency ventilation
  • Upgraded or replaced dilapidated or obsolete tunnel life safety systems with new CCTV cameras, Carbon Monoxide (CO) detectors, temperature monitors, fan controls, uninterruptible power supply units, and an integration system
  • Location on a main artery in urban Pittsburgh forced the majority of the work to occur during single-lane, nighttime closures (10 p.m. – 6 a.m.). This limited shift included the time to set up and take down the traffic control for the closures. Fourteen weekend full closures were given to the contractor to complete certain demolition and roadway repair work that could only occur in a traffic-free tunnel.

Sustainability Features & Outcomes

  • Installation of an oil water separator and storage tank for hydrocarbons to prevent storm water drainage from entering the Nine Mile Run Watershed - a design feature inspired by the AASHTO T-20 Tunnel Committee best practices. 

Awards & Recognition

  • National Recognition Award, 2016, American Council of Engineering Companies, Engineering Excellence Awards
  • Honor Award, 2016, American Council of Engineering Companies of Pennsylvania, Diamond Awards for Engineering Excellence
  • Rehabilitation Project of the Year, 2014, Engineers' Society of Western Pennsylvania, Project of the Year Awards
  • Award of Merit, 2014, American Society of Civil Engineers Pittsburgh Section, Engineering Achievement Awards.

Similar Projects: Engineering, Facilities: Structural, Transportation, Transportation: Tunnels