Project Description


Allegheny Tunnel
Somerset County, PA

The Allegheny Tunnel is located in Allegheny and Stonycreek Townships, Somerset County along the Pennsylvania Turnpike (I-70 / 76), a limited access highway, approximately 13 miles east of Exit 110 (Somerset, PA) and 23 miles west of Exit 146 (Bedford, PA).

The current westbound Allegheny Tunnel was constructed between 1938 and 1940 and was part of the 160 mile long “Original Section” of the PA Turnpike, which was largely designed to follow the abandoned South Penn Railroad right-of-way (ROW). The original Allegheny Tunnel was a one-tunnel, two-lane facility that needed to accommodate four-lanes of traffic.¬† As a result of increased traffic volumes and congestion, a second tunnel was constructed in 1965 south of, and adjacent to, the original tunnel. This new tunnel was constructed to carry two lanes of traffic in the eastbound direction. At the same time, the original tunnel was completely refurbished and modernized to carry westbound traffic.

In the late 1960’s, traffic congestion again became an issue at the westbound approach to the eastern portal of the tunnel. This was due to the steep grades ranging from 3.0% to 5.0% and the absence of a truck climbing lane approaching the tunnel. In response to the increasing traffic congestion in this area, the Pennsylvania Turnpike Commission added a third westbound lane between New Baltimore and the eastern portal of the Allegheny Tunnel with the right lane being designated as a truck climbing lane. As traffic volumes increased over the years, the merging of slower moving trucks from the climbing lane with faster moving vehicles from the two lanes that pass through the westbound tunnel became problematic and traffic congestion persisted. As an interim solution to ease this problem, the PTC re-designated the lanes in 1996 so that now trucks no longer have to merge left from the right lane before entering the tunnel. Instead, passenger vehicles traveling at similar speeds have to merge right from the left lane.

Since the construction of the new eastbound tunnel and the refurbishing of the original (westbound) tunnel in 1965, the Allegheny Tunnels and approaches have continued to be improved and modernized. These improvements include: alarm, lighting and vent control work; portal facade and signing work; tunnel lighting work; and installation of high mast lighting. In addition, in 1987 and 1988 both tunnels underwent major rehabilitation. An inspection conducted by the PTC in 1995 and 1996 revealed that the tunnels were rapidly deteriorating and were once again in need of major rehabilitation.

The Allegheny Tunnel Transportation Improvement Project was initiated by the Pennsylvania Turnpike Commission (PTC) in 1996 as a result of increasing concerns regarding:

  • Traffic Congestion
  • Frequency and severity of accidents in the vicinity of the tunnel
  • Physical and structural conditions of the tunnel
  • Rerouting of hazardous materials, which are prohibited in the tunnels, onto alternate routes

Five project needs were established in 1997 and several alternatives were developed based on the project needs and the numerous environmental studies that were conducted in the following years. The project was then placed on hold in 2001. After nine years it was re-initiated in 2010. Following the re-initiation of the project, the project needs were re-evaluated, alternatives were added to the south of the existing tunnel, and environmental studies were conducted. Six alternatives are currently being evaluated. They include the Brown Cut Alternative, Brown Tunnel Alternative, Yellow Cut Alternative, and Yellow Tunnel Alternative located north of the existing tunnel and the Gray Cut Alternative and Gray Tunnel Alternative located south of the existing tunnel. Each alternative is being evaluated with regards to environmental impact, engineering criteria, cost and public and agency input.  Examples of environmental studies conducted include: wetland and surface water delineation, threatened and endangered species habitat assessments, historic structures evaluation, archaeological predictive model update, geotechnical analysis, and general habitat assessments.

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  • Alternative Analysis
  • Wetland and Stream Identification and Delineation
  • Threatened and Endangers Species Survey
  • Habitat Assessment
  • Agency Coordination
  • Traffic Analysis
  • Geotechnical Engineering
  • Public Involvement
  • NEPA Documentation
  • Phase I Environmental Site Assessment and Mitigation