The crash took place around 6 a.m. Sunday northbound on I-95 just north of Exit 18 in Westport, said the Westport Fire Department on Facebook.
Arriving firefighters found a single car down an embankment and one occupant trapped inside. Firefighters extricated the occupant from the vehicle and then brought the person up the embankment utilizing a rope system, the department said.
All four of the occupants that were in the car at the time of the accident were transported to a local hospital.
The Fairfield Fire Department, Westport EMS, AMR and Norwalk Hospital EMS assisted on the scene.
The accident is under investigation by the Connecticut State Police.
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