A motorcyclist was in critical condition after hitting the back of a pickup truck Monday morning in Lake Grove, Suffolk police said.

Mark Ammirati, 49, of Selden, was on his Yamaha going west on Middle Country Road near Hawkins Avenue when he slammed into the back of a Toyota pickup truck just before 10:14 a.m., a crash that shut down westbound lanes for more than three hours, police said.

Witnesses said the pickup was stopped at the red light at the intersection with Hawkins Avenue, and why Ammirati did not stop was not immediately clear, said Det. Sgt. Dean Joseph of the Fourth Precinct.

"They said everybody was stopped and he's just moving," Joseph said.

Ammirati was taken to Stony Brook University Hospital, police said. The pickup driver was not injured, police said.

The westbound lanes were reopened at about 1:35 p.m., police said.

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Both vehicles were impounded for safety checks and the investigation continues, police said.

Detectives ask anyone with information to contact them at 631-854-8452.