It happened around Friday, Sept.11 at approximately 12:35 a.m. in West Islip.
The victim, a 23-year-old, was driving a 2016 Honda Accord eastbound on the Sunrise Highway Service Road, between West 3rd Street and West 4th Street, when the vehicle left the roadway, struck the guardrail and overturned, Suffolk County Police said.
The man, whose identity is being withheld pending notification of next of kin, was transported to Good Samaritan Hospital Medical Center in West Islip in critical condition.
Detectives are asking anyone with information on the crash to call the Third Squad at 631-854-8352.
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