The accident happened northbound on the Christina River Bridge.
One person was transported by Delaware State Police Helicopter from the scene to the Christiana Hospital Trauma Center with serious injuries.
Reports are that the injured person is the driver of a pickup truck that was towing a trailer.
The trailer became dislodged from the pickup and when the driver got out to attempt to reconnect it, he was struck by another vehicle.
He suffered multiple open fractures and abrasions.
I-495 northbound was completely shut down to traffic at Terminal Avenue for over two hours.