The 79-year-old man was taken to Holland Hospital by ambulance, where he died upon arrival, police said. His name was not immediately released pending notification of his death to his family.
The crash happened shortly before 11 a.m.
Shane Ayers of Holland Township was a passenger in the car behind the crash on southbound U.S. 31. Ayers thought the driver was falling asleep when his vehicle merged onto the shoulder near New Holland Street.
Then the 2011 Ford Fiesta drifted off the highway and into the ditch near Greenly Street. The car hit a small tree and rolled onto its side before coming to rest in a creek beyond the stand of trees, said Lt. Steve Kempker with the Ottawa County Sheriff's Department.
Ayers and his father pulled over to help the man, but found him unconscious.
The man was pinned in his smashed car and was extricated from it by Holland Township firefighters.
Sgt. Steve Austin said alcohol is not believed to have been a factor in the crash, and they are looking into a possible medical condition as the cause.
— From Grand Haven Tribune and Holland Sentinel reports