US lawFederal (United States)RegulationsTitle 49 CFR — TransportationChapter II — FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATIONPart 236 — RULES, STANDARDS, AND INSTRUCTIONS GOVERNING THE INSTALLATION, INSPECTION, MAINTENANCE, AND REPAIR OF SIGNAL AND TRAIN CONTROL SYSTEMS, DEVICES, AND APPLIANCESSubpart C — Interlocking236.37749 C.F.R. § 236.377Approach locking.Last amended: 2017Year: 2026Length: 31 wordsOfficial source Cite as 49 C.F.R. § 236.377 (2026)Approach locking shall be tested when placed in service and thereafter when modified, disarranged, or at least once every two years, whichever shall occur first. [49 FR 3385, Jan. 26, 1984]Previous49 C.F.R. § 236.376Next49 C.F.R. § 236.378