Police said the incident happened at 4:55 a.m. Wednesday on Route 112 near Barone Drive, critically inuring 53-year-old Grace Schmidt of Coram.
Schmidt "stepped into the southbound lane of Route 112, near Barone Drive, from the median and was struck by a 2018 Isuzu box truck," police wrote in a statement.
Schmidt was transported to Stony Brook University Hospital where she was admitted in critical condition, police said. The driver of the truck, John Paola, 21, of Mount Sinai, and his passenger were not injured, police added.
Police said the investigation is continuing and ask anyone with information to call the Sixth Squad in Selden at 631-854-8652.