Buses will replace some off-peak trains on the Montauk branch starting Monday because of rail testing, the Long Island Rail Road said.

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Sections of track will be taken out of service for testing through Thursday, and special schedules are available at terminals and stations or online at mta.info/lirr.

The testing is done by the Sperry rail car, which is designed to detect internal rail defects not readily visible to the eye. Defects that are found are corrected immediately by a crew of LIRR track maintenance workers, the LIRR said in a news release.