Switch installation work in Mineola is underway this weekend in preparation for the future third track between Floral Park and Hicksville.
While the work is underway, Huntington/Port Jefferson and Ronkonkoma Branch trains are being diverted to the South Shore via the Babylon and Central branches.
Travel times could be delayed as much as 60 minutes.
Oyster Bay trains will only run between East Williston and Oyster Bay. Passengers should use Babylon, Hempstead, Montauk or Point Washington branches instead to avoid delays.