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Smithton High-Level Bridge

Smithton High-Level Bridge

Primary Photographer(s): Nathan Holth and Rick McOmber

Bridge Documented: August 1, 2007

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Facility Carried / Feature Intersected
I-70 Over Youghiogheny River
Near Smithton: Westmoreland County, Pennsylvania: United States
Structure Type
Metal Continuous Rivet-Connected Warren Deck Truss, Fixed and Approach Spans: Metal 6 Panel Rivet-Connected Warren Deck Truss, Fixed
Construction Date and Builder / Engineer
1956 By Builder/Contractor: Unknown
Rehabilitation Date
Main Span Length
288.0 Feet (87.8 Meters)
Structure Length
1,355.0 Feet (413 Meters)
Roadway Width
64 Feet (19.51 Meters)
3 Main Span(s) and 5 Approach Span(s)
Inventory Number

Historic Significance Rating (HSR)
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Bridge Documentation

View Archived National Bridge Inventory Report - Has Additional Details and Evaluation

This bridge features 3 main spans that are a continuous deck truss following the Warren truss configuration. The end spans of the continuous sections are 216 feet, with the large center span over the river measures 288 feet. The remaining three main spans are simple 151.5 foot deck truss spans (which are 30 feet deep), also following the Warren truss configuration. Approach spans include a steel stringer span and a deck girder span.

This is an impressive bridge to view from below, and although it is a relatively late example of a continuous truss bridge, it should still be considered to have some historic value. The built-up members on this bridge have much more v-lacing and lattice than one would expect from a mid 1950s bridge.

 The bridge was rehabilitated (highly unusual for PennDOT), during which many rivets were replaced with bolts, and the deck was widened.


Information and Findings From Pennsylvania's Historic Bridge Inventory

Discussion of Bridge

The 8 span, 1,355' long Smithton Bridge built in 1956 consists of from the south a 52'-long, built up steel stringer span, a 3 span continuous Warren with verticals deck truss (1 @ 216', 1 @ 288', 1 @ 216'), 3 simply supported Warren with verticals deck truss spans (3 @ 151'-5") and a 100' deck girder span. The continuous truss spans are deepest over the bearings where the negative moment is greatest. Cantilevered deck sections are supported on built up brackets. The substructure consists of concrete abutments and column and cap beam bents. The engineering principals of continuous design were known and used since the late 19th century, but it did not become common until after World War II in Pennsylvania. This bridge is large, but it is a late example, and it has no innovative or distinctive details. It also uses common technologies. Neither the bridge nor its setting are historically or technologically significant.

Discussion of Surrounding Area

The viaduct carries a 4 lane, barrier divided highway and shoulders over 2 active CSXT railroad tracks (formerly B&O Railroad), which are also used by Amtrak on its Pittsburgh to Washington mainline; the Youghiogheny River, and a local road. On the river's west bank is the abandoned P&LE RR right of way. The setting is predominantly suburban, post-World War II residences. The area does not appear to have historic district potential. I 70, a second generation limited access highway in Pennsylvania, is not considered to be historically significant.

Bridge Considered Historic By Survey: No


Photo Galleries and Videos: Smithton High-Level Bridge


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Maps and Links: Smithton High-Level Bridge

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