Commuters on the Montauk branch of the Long Island Rail Road will be using buses for a part of their off-peak travel four days next week because of rail inspections, the rail service said.

Bus service will replace trains between Babylon and Speonk on Monday; east of Patchogue on Tuesday; east of Speonk on Wednesday; and between Babylon and Patchogue on Thursday so track inspections can be made using the Sperry rail car, the LIRR said in a news release.

The inspections use ultrasonic and induction test equipment designed to find internal rail defects not readily visible to the eye. On Monday and Thursday, inspections will run from 9:15 a.m. to noon. On Tuesday and Wednesday, inspections will run between 8:52 a.m. and 4:43 p.m.

The Sperry rail car is used twice a year to inspect about 500 miles of LIRR track, the LIRR said.

The rail service said customers should allow for up to 40 minutes additional travel time on Monday and Thursday and up to 90 minutes on Tuesday and Wednesday, depending on destination.

Here are details about Monday's altered schedule, between Babylon and Speonk:Eastbound: Customers traveling to Bay Shore, Islip, Great River, Oakdale, Sayville, Patchogue, Bellport, Mastic-Shirley and Speonk will take trains to Babylon, where buses will take them to their final destinations. Allow up to 23 minutes additional travel time.

Westbound: Customers who usually board trains at Patchogue, Sayville and Patchogue will instead travel by bus to Babylon, where train service will resume. Buses will depart up to 12 minutes later than usual train departure times and arrive at their destinations up to 40 minutes later.

Here are details about Tuesday's altered schedule, east of Patchogue:

Eastbound: The 8:52 a.m., 11:26 a.m. and 12:10 p.m. trains from Babylon will end at Patchogue. Customers will take buses at Patchogue for the remainder of the trip east to Speonk and Montauk. Travel time is expected to increase up to 41 minutes, depending on their destination.

Westbound: The 11:18 a.m. train from Montauk, the 2 p.m. from Speonk, and the 2:51 p.m. from Montauk will all originate from Patchogue, instead, at 1:07 p.m., 2:30 p.m. and 4:43 p.m., respectively. Customers at stations Montauk through Bellport will catch buses at their stations for travel to Babylon, where a train connection can be made for points west. Riders will board buses up to 50 minutes later than regularly scheduled train times and will arrive up to 90 minutes later, depending on their destination.

Here are details about Wednesday's altered schedule, east of Speonk:

Eastbound: The 8:52 a.m. and 12:10 p.m. trains from Babylon will end at Speonk. Customers will receive bus service at Speonk for the rest of their trip east to Montauk. Increased travel time could be up to 41 minutes, depending on destination.

Westbound: The 11:18 a.m. and the 2:51 p.m. trains from Montauk will originate from Speonk, instead, at 12:37 p.m. and 4:14 p.m. respectively. Customers at stations from Montauk through Westhampton will board buses at their stations for travel to Babylon, where a train connection can be made for points west. Customers will board buses up to 34 minutes later than their regularly scheduled trains and arrive up to 90 minutes later, depending on their destination.

Here are details about Thursday's altered schedule, between Babylon and Patchogue:

Eastbound: Customers traveling to Bay Shore, Islip, Great River, Oakdale, Sayville, Patchogue, Bellport, Mastic-Shirley and Speonk will go by train to Babylon, where buses will take them to their final destinations. Up to 23 minutes additional travel time is to be expected.

Westbound: Customers who usually board trains at Patchogue, Sayville, Oakdale, Great River, Islip and Bay Shore will instead take buses to Babylon, where train service will resume. Buses will depart up to 12 minutes later than usual train departure times and arrive at their destinations up to 40 minutes later.

Additional information is available in special Babylon and Montauk branch timetables or by calling 511, the New York State Travel Information Line (say, Long Island Rail Road). Customers can also go to mta.info/lirr.

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