TYNGSBORO -- A 40-year-old Dracut man is in critical but stable condition at a Boston hospital as a result of injuries he suffered when his car left Willowdale Road and struck a tree Tuesday afternoon, according to police.

Deputy Chief Richard Howe said Tyngsboro police were called to Willowdale Road near Willowdale Avenue about 5:30 p.m., and found a vehicle into a tree.

The man was the only person in the vehicle, and he was found unconscious and suffering from a severe head injury.

Howe said he is not being identified until his family has been fully notified.

He was taken to Lowell General Hospital and then transferred by ambulance to Brigham & Women's Hospital in Boston.

Howe said alcohol does not appear to be a factor, but the reason the car left the road is under investigation.

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