Work on the double-track project on the Ronkonkoma branch will cause service disruptions during the next two weekends, the LIRR said.

Buses will substitute for trains at Wyandanch, Deer Park, Brentwood, Central Islip and Ronkonkoma stations from 11:59 p.m. Friday to 4 a.m. Monday on those weekends, the railroad said.

Riders using the affected stations should plan for as much as 44 minutes of added travel time, or should consider using the Babylon branch or Port Jefferson branch, with half-hourly service, the railroad said.

There may also be only a single lane of vehicular traffic at some crossings during the weekends, the railroad said.

On these two weekends, the last arriving train Saturday morning at Farmingdale before the start of construction work will be the 12:48 a.m. from Ronkonkoma, the LIRR said.

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Service on that stretch of track following the weekend work will resume on both Monday mornings at 12:46 a.m., with departures at both Farmingdale and Ronkonkoma stations.

The 4:39 p.m., 5:39 p.m. and 6:39 p.m. trains from Penn Station, as well as the 10:05 a.m., 11:05 a.m. and 12:05 p.m. originating in Ronkonkoma, will not be running on these weekends.

The double track project will add a second track to the 18-mile stretch from Farmingdale to Ronkonkoma by the end of next year at an estimated cost of $387 million.