A 23-year-old man who rear-ended another vehicle in Aiea lost consciousness after the crash, possibly because of head injuries, police said.

The man, who was driving a 2009 black Scion, went to the Queen’s Medical Center in critical condition last night.

The accident happened at about 7 p.m. on Kamehameha Highway near McGrew Loop. Police said the Scion, traveling east, rear-ended a 2003 black Honda Odyessy driven by a 50-year-old woman.

When both drivers pulled over to the right to exchange information, the woman noticed the Scion driver going in and out of consciousness, police said.

Alcohol and speed are not factors and both drivers were wearing seat belts, police said.