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photo of bridge

View west on Viaduct Number 1

photo of bridge Panoramic view north from Viaduct Number 1

More detail photos

P. J. McArdle Roadway, Viaduct 1 (over Norfolk Southern Railroad)
P. J. McArdle Roadway, Viaduct 2 (over ravine at Arlington Av)

Lower McArdle Roadway
Mt. Washington Roadway


USGS 7.5" Topo Quad - UTM Coordinates:
Pittsburgh East - Zone 17; 0585 4475
Lower P. J. McArdle Roadway [formerly Mt. Washington Roadway]

-- Arlington Av [formerly Brownsville Rd]
-- South Ninth St; Bradish St

-- Viaduct 1: Norfolk Southern [former PRR]
-- Viaduct 2: ravine at Arlington Av [aka New Arlington Av]

Over railroad: steel through camelback Pratt truss
Viaducts: steel deck girder with trussed bents

Viaduct 1 through truss: 220 ft est

TOTAL LENGTH (including longest elevated ramp):
Viaduct 1: 546 ft, including 11 spans on trussed bents, 10 ft pier and through truss
Viaduct 2: 372 ft, including 9 spans on trussed bents
26 ft wide roadway, with 6 ft wide sidewalk to south


1933-1935, City of Pittsburgh


excerpt from Frederick Law Olmsted report to The Pittsburgh Civic Commission, 1910:

South Hills Artery

Between the Point District and the South Hills Artery there is now urgent need for a thoroughfare connection of adequate capacity and on reasonable gradients. At present the only access for surface traffic -- except electric cars -- is via the Brownsville Road [now Arlington Av], or South Eighteenth Street, or the inclines. The two roads are steep, from 7 to 8 per cent, and the inclines are expensive and of very limited capacity. The South Hills country is sparsely developed as yet, but, being comparatively free from smoke and very near to the business district, it offers unusually desirable opportunities for homes, and it must soon be thickly settled. The need for a good thoroughfare to this region will then be of far greater importance even than now.

Only two reasonable ways of securing such a thoroughfare appear. One is by a new slanting road up the hillside south of the river, much longer, and so on an easier gradient, than Brownsville Road; the other is by some high-level bridge and tunnel scheme, such as that proposed by residents of the South Hills.

The opportunities for a hillside road have been studied with some care, but the excessive length required to get a reasonable gradient, and the difficulties and high cost of constructing a wide thoroughfare on the steep hillside, have proved to be serious drawbacks to all possible plans for such a street.


Owing to the importance of the South Side as a point for the delivery of freight, a reasonably direct and easy approach from there to the new tunnel seems desirable. Freight to be teamed to the South Hills District seems likely to originate either near the Smithfield Street bridge, or east of South Seventeenth Street. From the former point, it is almost out of the question to get an approach of easy gradient to the mouth of the tunnel, on account of the lack of distance; but it must be remembered that the inclines will still be available, greatly relieved by the new tunnel from their present congestion, and further that freight for the South Hills could easily be shipped to points from which access to the new tunnel would be easy and direct. From the latter point, the connection can be secured by climbing over the railroad on a viaduct, probably along South Twelfth Street, and thence following the hillside westward on a more or less uniform gradient to the mouth of the tunnel. An examination of the hillside below the Brownsville Road indicates that such a street, though somewhat costly, is not in the least impracticable. It might be best to construct it with a minimum of cutting by the use of a side-hill viaduct of reinforced concrete.

Such was the situation that led to the construction of the Liberty Tunnels (1924) and the Liberty Bridge (1928) to provide a direct route between downtown and the South Hills. But the choice of a high-level tunnel location, as compared with one which connected to Carson St, did not improve matters on the flats of the South Side, nor help the 400-foot climb up the face of Mt. Washington.

A 1916 Hopkins plat map shows a proposed Mount Washington Roadway, but not the Liberty Tunnels and Bridge; each plan had its backers, but possibly not a consensus which included both. The tunnels and bridge were constructed by Allegheny County; the City of Pittsburgh was responsible for building the Mt. Washington Roadway. The year after the bridge opened, the city completed the upper section of the hillside roadway between a traffic circle at the northern tunnel portal and Grandview Av atop Mt. Washington.

As described by Olmsted, the lower section of the Mount Washington Roadway was intended to open up the western end of the South Side. Even today the intersection of Arlington Av and Carson St is constricted by the multiple railroad overpasses which force a narrow and tight turn for South Side traffic. It appears the bottom portion of Arlington Av was raised and reconstructed to facilitate the intersection of the Mt. Washington Roadway; the poor soil quality in the filled area would be a problem when the road required repairs in 2000. And the importance of this traffic connector would be demonstrated during a three year closure.

The 1916 Hopkins map and 1935 construction photos show Manor St adjacent to and at the same elevation as the railroad. Where the slope of Brownsville Rd crossed the plane of Manor St the streets formed a sharp interection; within this acute angle stood the Knox Public School. The 1916 map proposed the new roadway would follow Manor St precisely. In the construction photos, the school is shown just south of where the Mt. Washington Roadway was finally located.

In locating the new roadway about 90 feet south of Manor St, the new roadway had to be elevated and terraced onto the hillside. At the intersection of the new roadway and Brownsville Rd, construction at the higher elevation was satisfied by the construction of Viaduct Number 2: a 372 foot long series of nine short girder spans on trussed bents. When this structure was inspected in 2000, after 65 years of service, it was found to be too dangerous to remain open to traffic. Perhaps engineers were wishing the alternate 1935 design of a terraced roadway atop a retaining wall had been used; disagreements between PennDOT (now providing some 95% of the repair funding) and the City caused the project to be delayed for three years. PennDOT engineers and consultants determined the poor quality of soil beneath Viaduct Number 2 would not provide reliable support without the inclusion of new piling. Had the terrace design been used, this problem would not have occurred.

Viaduct Number 2 is also interesting in that it has a sharp, nearly 90 degree curve, at the intersection with Arlington Av.

East of Viaduct Number 2, the roadway was built on a terrace above a retaining wall. Some of the foundations and walls of homes which once stood along Manor St and Brownsville Rd may still be seen. During the three year closure (2000-2003), this stretch of about one-quarter mile became severely overgrown.

Viaduct Number 1 was built between Windom St and South Ninth St. The viaduct is 546 feet long with a through truss span over the railroad and a series of 11 short girder spans on trussed bents. The camelback Pratt through truss is about 220 feet long. Each of the shorter spans is about 33 feet long with simple and continuous spans.

Near the South Seventh St, the structure features a horizontal curve. This "correction" comes from the meeting of two street grids: South Sixth St once formed boundary between South Pittsburgh and Birmingham, with each former borough having its streets aligned with respect to the Monongahela River.

The 1916 Hopkins map proposed the route would align with Sarah St and land at the intersection with South Seventh St. As built, Viaduct Number 1 lands at South Ninth St aligned with Bradish St; Bradish St was renamed as part of the Roadway for the block leading to South Tenth St. This extension creates a logical connection with the South Tenth St Bridge leading over the Monongahela River into downtown.

Despite the size of the viaduct and through truss, the structure snuggles into the hillside below Windom St -- the faded green paint nearly fades into the tree-covered green. But Viaduct Number 1 offers an impressive panoramic view of the downtown skyline sweeping eastward across Duquesne University on the Bluff, the gleaming domes of St. John's church, the golden suspension catenary and towers of the South Tenth St Bridge, over the densely-packed low-rise buildings of the South Side flats, beyond the massive Birmingham Bridge and further upstream to the big bend on the Monongahela.


Peter J. McArdle (1874-1940) was first elected to Pittsburgh City Council in 1911; one source notes he served for over 27 years. He was a member of the City Planning Commission when the Mt. Washington Roadway was being discussed in 1912. Previous to public office he had worked in a rolling mill and was active in union councils within the steel industry. A funeral notice indicates his home was on Bigham St, Mt. Washington.


field check; 1916 G.M. Hopkins plat map; Tribune Review; Kelly, Allegheny County: a sesqui-centinnial review, 1938; Rook, Western Pennsylvanians: A work for newspaper and library reference, 1923; Larry Woods

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Introduction -- Nearby Structures

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Last modified: 14-May-2003

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