A truck carrying metal fencing rolled over, closing the exit 13 southbound on-ramp from the Wharton Brook Connector to Interstate 91 in Wallingford.
State police expect it to be closed for several hours during the cleanup.
The rollover also closed the northbound on-ramp, but that side has reopened.
No injuries were reported at the scene.
The state Department of Transportation, Wallingford EMS and the fire department are at the scene.