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Squirrel Hill Tunnel
763-4-1, 870+00 west portal
763-4-1, 912+25 east portal



USGS 7.5" Topo Quad - UTM Coordinates:
Pittsburgh East - Zone 17; 0591 4475 western portal; 0592 4475 eastern portal
Interstate 376, US22, US30 [Penn Lincoln Parkway East] two lanes each bore; emergency walkway on inner wall

-- Penn Lincoln Parkway East - Squirrel Hill interchange
-- Penn Lincoln Parkway East - Nine Mile Run valley and Commerical St Bridge

Squirrel Hill
two bores, circular roof with flat plenum ceiling;
concrete with ceramic tile lining;
8 cross passages

4,225 ft

13ft 6 in posted vertical clearance
28 ft wide (est)

1946-1953 (opened June 5, 1953), PA Dept of Highways

PennDOT, current owner
At a cost of $18 million, it was the most costly single project built by the State Highways Department and completed the last link in the first eight mile section of the Parkway.

Contractors for the project: B. Perini & Sons, Inc., of Framingham, MA (tunnel excavation, supports, lining, drainage, concrete base for roadbed, Sep 1948 to Jul 1951); Washington Engineering and Construction Co, of Washington, PA (ventilation buildings, heating ventilation and plumbing systems, Sep 1950 to Apr 1953); Atlas Tile & Marble Works, Inc. of New York, NY (tile, railing, drainage, brick paving, signs, markers, plaza paving, Mar 1951 to Sep 1952); Westinghouse Electric Corp, of Boston, MA (fans, motor and transmissions for ventilation buildings, Feb 1951 to Jun 1953); Electro Construction Co, of Philadelphia, PA (conduit, wiring, insulation and lighting equipment, all other electrical work, Apr 1951 to Jul 1953).

The Squirrel Hill Tunnels are similar in design to the Fort Pitt Tunnels on the Parkway West and the Lehigh Tunnels on the Northeast Extension of the PA Turnpike which were constructed at about the same time.

The Squirrel Hill Tunnels and Parkway East were delayed by the Second World War; design details hint at the compromises required. At Squirrel Hill the maintenance and ventilation buildings at each portal are faced in peach brick, while the Fort Pitt Tunnel (1957-1960) received two colors of polished granite. The off-white tile, lighting, stainless steel doors and fittings of the interior of each are nearly identical.

Of the highway tunnels in Allegheny County, the Squirrel Hill Tunnels (4,225 ft) are second in length to the Liberty Tubes (5,889 ft), ahead of the Fort Pitt (3,614 ft).

PennDOT lists the following facts: 2,312 light fixtures with 4,624 bulbs; 8 ventilation fans; 219,700 sq ft tiled surface to wash; cross-section area 392 ft; serving nearly 106,000 vehicles per day

The twin-bore follows a constant 2.5 percent grade rising from east to west. This grade assisted in drainage during the excavation. The blasting progressed from the east and most of the excavated material was deposited to a depth of 100 feet in the 1,000 feet between the eastern portal and the Commercial St bridge. A lesser amount of material was used to fill the interchange area at Forward Av.

view page - More history of the location of the Parkway and the Squirrel Hill Tunnel.

Pittsburgh's east suburban traffic is measured from the Squirrel Hill Tunnel. Morning and evening rush hours each form their jam from this location: typically stretching eastward to Churchill in the morning and westward to the Blvd of Allies.

excerpt from 1953 PA Dept of Highways report
The tunnel consists of two parallel tubes sixty feet on centers, each carrying two twelve-foot, one-directional traffic lanes, leaving a twenty-seven foot core of unmolested ground between them. Its length, face to face of portals, including transition and cut and cover sections, is 4,225 feet. The clear width of each tube is twenty-nine feet one and three-quarters inches, including the curb and sidewalk section, with a vertical clearance of fourteen feet two inches from paving crown to roadway ceiling. The tunnel ceiling is circular in shape, with a radius of nineteen feet three inches. The ceiling rise in the south tube, above the roadway ceiling, is five feet nine and a half inches and that in the north tube is six feet six and a half inches, thus giving the north tube a larger airduct which is required to properly ventilate the ascending grade of two and a half per cent.

Design Features:
The design was based on subsurface evaluations made from conventional borings which revealed rather poor ground would be encountered in driving the tubes. Permanent steel supports were provided. Vertical posts and arch rings are eight-inch I-beams with six-inch channel lagging. The spacing of sets of steel supports and lagging varied with the with the stability and nature of the ground encountered. The steel sets ranged from two to five feet on centers and the lagging were placed from skin tight to two feet apart.

The concrete side walls are twenty-seven inches, basic thickness, reinforced vertically and horizontally. The tunnel arch ceiling is also reinforced both longitudinally and circumferentially. The six-inch reinforced concrete roadway ceiling rests on sidewall haunches and is suspended at the center with three-inch by three quarter-inch stainless steel hangers spaced ten feet six inches apart along the center line and anchored in the tunnel ceiling.

Grout was placed outside the tunnel lining, through steel grout and vent pipes, to impregnate, strengthen, and watertight porous, weak and shattered rock adjacent to the tunnel, also to fill rock seams and voids outside and near the tunnel walls. The number of grout pipes placed in the concrete lining depended on the extent of excavation overbreak, amount of dry-packing and the general condition of the ground as to seams, moisture content and stability. Grout was pumped at pressures ranging from ten to 100 pounds per square inch, depending on location and how freely it was received.

Roadway Pavement:
The ten-inch reinforced concrete roadway base rests on a twelve-inch well graded special substrate material compacted in two courses. The wearing surface is buff colored de-aired vitrified fire clay brick (since replaced by concrete) laid on a three quarter-inch mastic cushion. A line of vitreous white-bodied ceramic brick, of the same dimension as the paving brick, was placed longitudinally in the center of each tunnel, thus forming a permanent marker between traffic lanes.

The sidewalls are finished with light ivory ceramic vitreous glazed tile four and a half inches square and three-eighths to nine-sixteenths of an inch thick, including the projecting anchor lugs. The sidwalks blend well with the ceiling which has been painted with a synthetic resin base paint, and slightly lighter in color than the walls.

The tunnels are are well drained by an eighteen-inch triple-strength vitrified clay longitudinal storm sewer under the roadway in each tube to which a system of laterals carry water from the twelve-inch to twenty two-inch stone drains immediately back of each footing, from the three-inch asbestos cement ceiling drains, the small curb gutter and the roadway gutter.

Ventilation System:
The tunnels are ventilated by two blow and two exhaust fans in each ventilation building. Each fan is powered by a large and a small motor with a single transmission. Hence, regardless of which motor is driving the fan, the other motor drags. With three speeds within the ability of two motors, the proper selection of speed is governed by the ventilation required. When exhaust is chosen, foul air is drawn from the tunnel through the roadway ceiling air ports, then through the air duct and out the evase stack. When blow is applied, fresh air is received through the louvers at the rear of the buildings, forced through the air duct and into the tunnel through the roadway ceiling air ports. The design of the ventilation system was reviewed and approved by the U.S. Bureau of Mines.

Through copper sampling pipes, extending into the tunnels, vacuum pumps draw a continuous flow of air into the analyzing rooms. The amount of carbon monoxide present is automatically and continuously recorded on graphic charts. In case the carbon monoxide exceeds the preset valve (sic), a suitable and effective warning attracts the attention of the attendant who may immediately increase the ventilating effort. Other automatic controls, such as the fire alarm, overheight signals and heating, contribute to precision of operation with minimum effort.

The ventilation buildings, one at each end of the tunnel, are nearly identical in design, varying only to fit field conditions and equipped individually to function efficiently. They are constructed of reinforced concrete to the elevation of the electrical floor and above this point structural steel framing encased with concrete with concrete for fire protection. The portals are veneered with a cross-grain sawed grayish colored sandstone, to the electrical floor, which blends with the buff-colored brick above this point.

The tunnel is lighted by continuous six foot long fluorescent lamps on each side of the tube, two of which are inserted in a frosted pyrex tube twelve feet four inches long, having an outside diameter of two and a half inches and extending from transformer to transformer. The lighting is divided into two sections, namely, the intensive zone starting at the entrance portal and extending 1800 feet into the tunnel, and the normal lighting zone extending from the end of the intensive zone to the exit portal. The intensive zone is divided into four zones, each of which is controlled by a separate rheostat for daytime and night operations. The highest intensity exists at the entrance portal, with each succeeding zone diminishing in intensity until that of the normal lighting is approached.


fieldcheck; 1953 PA Dept of Highways report; PennDOT District 11 website; Lorant: "Pittsburgh: The Story of an American City"; Pittsburgh Post-Gazette

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Introduction -- Nearby Structures

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Last modified: 25-Jul-2001

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