Allegheny Tunnel

Traveling Construction Allegheny Tunnel

Transportation Improvement Project

Project Overview

Allegheny Tunnel - Transportation Improvement Project
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 approximate center of the project area is located at Latitude 39 57' 47.3" North and Longitude -78^ 51' 02.8" West.
Allegheny Tunnel - Transportation Improvement Project

The Allegheny Tunnel Transportation 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.

  • Transportation Demand
  • Existing Geometric Constraints
  • Accident Rates
  • Tunnel Conditions
  • System Linkage and Continuity (Diversion of Hazardous Material Haulers)

Multiple alternatives were developed based on the project needs and numerous environmental studies 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 were evaluated. They included 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 was evaluated with regard to environmental impact, engineering criteria, cost and public and agency input.  After much evaluation, it was determined there were no Project alternatives that completely avoided environmental impacts, met all Project purpose and needs, and provided for reasonable costs. 

The Gray Cut Alternative was selected as the Project Preferred Alternative as it best balances all the operational, safety, cost, and environmental considerations that are components of the Project.  As noted, the Gray Cut Alternative is not without environmental impacts; therefore, federal and state permits will be required.  Please refer to the Environmental Document for more detail.

With the selection of the Preferred Alternative, the Alternatives Analysis phase of the Allegheny Tunnel Transportation Improvement Project is complete, and the project is moving into the Preliminary Design phase early 2023.


Allegheny Tunnel History

1938-1940The current westbound Allegheny Tunnel was constructed 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 South Penn Railroad tunnel, which was never completed, is located immediately adjacent to, and north of, the existing Allegheny Tunnel. 

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.

Late 1960s - 1988Traffic 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. The Allegheny Tunnels and approaches continued to be improved and modernized including alarm, lighting and vent control work; portal façade and signing work; tunnel lighting work; and installation of high mast lighting.  In 1987 and 1988 both tunnels underwent major rehabilitation.

The PTC conducted an inspection of the tunnels in 1995 and 1996.  It revealed the tunnels were rapidly deteriorating and were once again in need of major rehabilitation.  As a result, the Allegheny Tunnel Transportation Improvement Project was initiated.

In addition, 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.
2003-2010The following improvements took place: drainage repair, fire pump replacements, roof replacement of portal buildings, lighting replacement, fan housing replacement, and substation construction.
2011-2015General rehabilitation and electrical upgrades occurred.
2020-2021Lighting and conduit replacement occurred.


Project Needs

  • Transportation Demand
  • Existing Geometric Constraints
  • Accident Rates
  • Tunnel Conditions
  • System Linkage and Continuity (Diversion of Hazardous Material Haulers)

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