US lawFederal (United States)RegulationsTitle 23 CFR — HighwaysChapter I — FEDERAL HIGHWAY ADMINISTRATION, DEPARTMENT OF TRANSPORTATIONPart 650 — BRIDGES, STRUCTURES, AND HYDRAULICSSubpart E — National Tunnel Inspection Standards650.50323 C.F.R. § 650.503Applicability.Last amended: 2017Year: 2026Length: 32 wordsOfficial source Cite as 23 C.F.R. § 650.503 (2026)The National Tunnel Inspection Standards (NTIS) in this subpart apply to all structures defined as highway tunnels on all public roads, on and off Federal-aid highways, including tribally and federally owned tunnels.Previous23 C.F.R. § 650.501Next23 C.F.R. § 650.505