Authorities say 16-year-old Eric Albrecht of East Moriches suffered a broken hip and other injuries.
The LIRR says he was walking along the tracks in Center Moriches around 1 p.m. Monday as a Montauk train approached.
According to Newsday, MTA police said the train was traveling about 60 mph, below the maximum allowable 65 mph.
LIRR spokesman Salvatore Arena says the engineer sounded his horn but Albrecht apparently didn't hear it. He says the engineer brought the train to an emergency stop.
Center Moriches Fire Chief Ron Primus says Albrecht landed in a ravine off the side of the tracks.