Brian Donahue, 50, of Burlington, was taken to Hartford Hospital to be treated for severe head and leg injuries, police said.
His motorcycle collided with a tan four-door sedan driven by Maria Arcari, 73, of Newington. Arcari was not taken to the hospital.
Route 4 was closed for at least four hours during the accident clean-up. The North Central Municipal Accident Reconstruction Squad, which was on scene Wednesday night, continues to investigate the cause and circumstances of the accident.
Police ask that anyone with more information about the accident contact the department at 860-675-2400.