THE A12 was blocked after a five-vehicle collision.
The incident occurred at 6.25pm on the northbound carriageway at junction 27, at Spring Lane, Colchester.
Traffic was queueing back to junction 26, at Eight Ash Green, while emergency services attended the scene.
One ambulance was called, along with a Hazardous Area Response Team.
An East of England Ambulance Service spokeswoman said medics were treated four patients for slight injuries at the scene.
One patient was taken to Colchester General Hospital.
The carriageway was due to be reopened by Essex Police by 7.15pm.