{"nrhp_refnum":"81000211","name":"Airtight Bridge","other_names":["Bridge Number 3165"],"category":"structure","location":{"address":"NE of Charleston","address_restricted":false,"city":"Charleston","county":"Coles County","state":"IL","lat":39.54913270600008,"lon":-88.09330098999999,"geom_source":"nps_gis"},"listed_date":"1981-11-30","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Engineering","Transportation"],"significance_levels":["local"],"summary":{"what_it_is":"A steel Pratt through-truss highway bridge, 188 feet long, carrying township road 275 over the Embarras River about 8 miles northeast of Charleston, Coles County, Illinois. It was built in 1914 by the Decatur Bridge Company to a design by Claude L. James.","why_significant":"The bridge is the only river crossing in Coles County between Quarry Bridge and the north county line, about 12 miles. It is also a fine example of the simple Pratt truss, showing how early 20th-century engineers returned to a simpler design once steel and better engineering knowledge made extra members unnecessary. It is the newest and simplest bridge in its thematic group.","narrative":"Built in 1914 by the Decatur Bridge Company to a design by Claude L. James, this 188-foot steel bridge carries a township road over the Embarras River northeast of Charleston, Illinois. Its main span is an eight-panel Pratt through-truss, pinned and riveted, with a concrete floor, a pony truss approach on the west and a steel beam approach on the east. The site was once known as Willow Pond Ford, and the bridge is the only crossing of the river in the northern half of the county. Local folklore offers two explanations for the name Airtight: stagnant air settling in the surrounding valley, or old cars stalling on the steep eastern hill because of the position of their gasoline tanks. The bridge matters as a clear example of the simple Pratt design, which engineers returned to after earlier bridges added redundant members. It is the newest and simplest of the Embarras River bridges in its group.","period_of_significance":null,"architect_builder":"Claude L. James (engineer); Decatur Bridge Company, Decatur, IL","architectural_style":"Pratt through-truss","criteria":[],"status_note":"Described as in fair condition, with a load limit of eight tons.","vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:35.106931-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/opastorage/live/95/8907/28890795/content/electronic-records/rg-079/NPS_IL/81000211.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/81000211/2c523b9466-800.webp","url_1600":"https://nationalhistoricalregister.com/media/81000211/2c523b9466-1600.webp","licence":"Public domain","author":"Nyttend","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Airtight_Bridge.jpg\" rel=\"noopener\">Nyttend</a>, Public domain, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Airtight_Bridge.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/28890795","wikipedia":"https://en.wikipedia.org/wiki/Airtight_Bridge","wikidata":"https://www.wikidata.org/wiki/Q4699044"},"indexable":true,"url":"https://nationalhistoricalregister.com/illinois/coles-county/airtight-bridge-81000211/"}