WFR responded to a single tractor/trailer rollover on I-29 yesterday evening.  The accident took place around Mile Marker 174 in the north bound right of way.  The tractor became unattached from the trailer during the incident.  The tractor was pulling a ferris wheel for a carnival company.  One patient was treated by WFR EMS and then transported to Prairie Lakes Hospital.  Rescue 51 cleaned up debris and assisted  EMS.  The accident is still under investigation by the SD highway Patrol.