An environmental assessment is under way for the project. Public hearings and information sessions also are planned.
The Ronkonkoma Branch links the LIRR's Main Line in Hicksville to points in eastern Long Island, terminating in Greenport, N.Y., on the island's North Fork. Diesel locomotives protect service east of Ronkonoma, which serves as a transfer point.
LIRR President Helena Williams said the double-tracking project would allow "half-hourly service with two tracks" for service to and from Manhattan, noting, "Two tracks are better than one." She added, "Right now with one track, if a train becomes disabled or there's the need for police activity on a train then, unfortunately, every train after that backs up."
Williams was joined by U.S. Sen. Charles Schumer (D-N.Y.) in making the announcement.
Ridership has doubled on the Ronkonkoma branch in the past 25 years, LIRR says. Third-rail electrification was added to the route in December 1987, but numerous attempts to increase track capacity since then have stalled or been deferred.
The railroad seeks to complete phase one of the project by 2016.