{"nrhp_refnum":"88000796","name":"Colwell Cut Viaduct","other_names":["Hogback Hill Bridge"],"category":"structure","location":{"address":"LR 66 over Pittsburgh & Shawmut RR","address_restricted":false,"city":"Seminole","county":"Armstrong County","state":"PA","lat":40.937050154000076,"lon":-79.36290180599997,"geom_source":"nps_gis"},"listed_date":"1988-06-22","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Engineering"],"significance_levels":["state"],"summary":{"what_it_is":"An open-spandrel concrete arch bridge carrying Hogback Hill Bridge highway traffic over the Pittsburgh & Shawmut railroad at Seminole, Mahoning Township, Armstrong County, Pennsylvania. It was built in 1922 by the Concrete Steel Bridge Company of Clarksburg, West Virginia.","why_significant":"The nomination describes the bridge as a typical example of the open-spandrel concrete arch type. Its 128-foot main arch is of moderate length within the nominated group. It is one of only four nominated concrete arch bridges in western Pennsylvania and one of only a few nominated bridges to exemplify this type in that region. The area of significance is engineering.","narrative":"Built in 1922 by the Concrete Steel Bridge Company of Clarksburg, West Virginia, the Colwell Cut Viaduct is an open-spandrel concrete arch bridge that carries vehicular traffic over the Pittsburgh & Shawmut railroad in rural Mahoning Township, Armstrong County. Its main arch spans 128 feet, placing it within the range of the open-spandrel arches in the nominated group, which run from about 40 to 200 feet. The bridge is known locally as Hogback Hill Bridge and is listed as Structure No. 99 in its inventory records. Its boundary covers the superstructure and substructure within the outside corners of the wing walls, and the site is less than one acre. Its importance lies in engineering. It is one of only four nominated concrete arch bridges in western Pennsylvania and one of only a few nominated bridges in the region that represent this widely used concrete type. In 1975 its parapets and deck were replaced, which reduced its original integrity.","period_of_significance":"1922","architect_builder":"Unknown (designer/engineer); Concrete Steel Bridge Co. (bridge company)","architectural_style":null,"criteria":["C"],"status_note":"Parapets and deck were replaced; the structure was altered in 1975.","vacant_flag":null,"machine_generated":true,"model":"claude-haiku-5-5","prompt_version":"v1.1-2026-10-29","generated_at":"2026-10-29 17:11:37.93283-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_PA/88000796.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/88000796/3dda1a58fd-800.webp","url_1600":"https://nationalhistoricalregister.com/media/88000796/3dda1a58fd-1600.webp","licence":"Public domain","author":"PennDOT","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Colwell_Cut_Viaduct.jpg\" rel=\"noopener\">PennDOT</a>, Public domain, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Colwell_Cut_Viaduct.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/71992260","wikipedia":"https://en.wikipedia.org/wiki/Colwell_Cut_Viaduct","wikidata":"https://www.wikidata.org/wiki/Q5150319"},"indexable":true,"url":"https://nationalhistoricalregister.com/pennsylvania/armstrong-county/colwell-cut-viaduct-88000796/"}