Four people were sent to the hospital on body boards, and another three were also sent to the hospital after a Thursday evening rollover accident on Mystic Valley Parkway in Somerville.
The accident happened at about 5:20 p.m. at the intersection of Mystic Valley Parkway (Route 16) and Boston Avenue, near the border of Medford.
Somerville and Medford fire departments responded to the scene along with police departments from both communities and Massachusetts State Police.
Police officers closed off nearby sections of Route 16 and Boston Avenue so emergency personnel could attend to the victims.
The accident happened during rush hour, and fire trucks had to fight their way through gridlock to get to the scene, said District Chief Frank Lee of the Somerville Fire Department.
Once on the scene, "We backboarded four people and there were three that were not backboarded," he said.
"Two of them were seriosuly injured," the district chief said. Some of the victims were transported to Massachusetts General Hospital and the others went to Lawrence Memorial Hospital in Medford.
This busy intersection is a dangerous one. "Something like this happens four or five times a year," Lee said, adding that firefighters respond to minor accidents at the intersection two or three times a month.