{"nrhp_refnum":"88000733","name":"Campbell's Bridge","other_names":[],"category":"structure","location":{"address":"Allentown Rd. over Unami Creek","address_restricted":false,"city":"Milford Square","county":"Bucks County","state":"PA","lat":40.42856864000004,"lon":-75.39784979299998,"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":"Campbell's Bridge is a concrete open-spandrel ribbed arch vehicular bridge carrying Allentown Road over Unami Creek in Milford Township, Bucks County, Pennsylvania. It has a single 72-foot segmental arch span.","why_significant":"The nomination argues the bridge is an important early example of the open-spandrel arch form in concrete. It is described as a very good example of the transition from solid filled barrel arches to ribbed open-spandrel arches. It is the earliest of fifteen open-spandrel arches included in the group nomination, and its thin parapet is said to recall older camelback stone arch bridges. The area of significance is engineering.","narrative":"Campbell's Bridge is a single-span concrete arch carrying Allentown Road over Unami Creek in Milford Township, Bucks County. Built in 1906, its segmental arch spans 72 feet and is carried on two thick ribs that are linked by transverse arches, which transfer the deck loads to the ribs. The open spandrels reduce the mass of the structure compared with earlier solid-filled barrel arches. Its builder is not recorded. The bridge is considered an early and very good example of the shift from solid barrel arches to ribbed open-spandrel arches in concrete, a decade of experimentation in the material. The surface of the arch is plain, without incised decoration, and the thin flat parapet rising to a gentle point recalls earlier camelback stone bridges. The bridge is the earliest of fifteen open-spandrel arches included in the group nomination. Its engineering significance rests on this place in the development of concrete arch design in Pennsylvania.","period_of_significance":"1906","architect_builder":null,"architectural_style":null,"criteria":["A"],"status_note":"Unaltered, with the vehicular use continuing at present according to the form.","vacant_flag":false,"machine_generated":true,"model":"claude-haiku-5-5","prompt_version":"v1.1-2026-10-29","generated_at":"2026-10-29 17:11:37.064137-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_PA/88000733.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/88000733/bf63411790-800.webp","url_1600":"https://nationalhistoricalregister.com/media/88000733/bf63411790-1600.webp","licence":"Public domain","author":"Joseph Elliott","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Campbell%27s_Bridge,_Spanning_Unami_Creek_at_Allentown_Road_(State_Rout,_Milford_Square_vicinity_(Bucks_County,_Pennsylvania).jpg\" rel=\"noopener\">Joseph Elliott</a>, Public domain, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Campbell%27s_Bridge,_Spanning_Unami_Creek_at_Allentown_Road_(State_Rout,_Milford_Square_vicinity_(Bucks_County,_Pennsylvania).jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/71992450","wikipedia":"https://en.wikipedia.org/wiki/Campbell%27s_Bridge","wikidata":"https://www.wikidata.org/wiki/Q5027957"},"indexable":true,"url":"https://nationalhistoricalregister.com/pennsylvania/bucks-county/campbells-bridge-88000733/"}