Senior Constable Bruce Dow, of Oamaru, said police and crash workers were at the site on January 4.
A car towing a caravan on State Highway 8 near Omarama crashed after a crosswind appeared to lift the dual-axle caravan, causing the car to fishtail and crash down a 2m bank.
He said accident signs and road cones were set up at each end of the crash scene and there were large recovery vehicles as well as a police vehicle parked there.
Snr Const Dow and a road contractor, dressed in safety vests, then struggled to control traffic as it shot through the area, even though he and the contractor ''were sticking out like sore toes''.
He said it got so bad he and the other man physically intervened by waving vehicles down and informing motorists of their obligation under the law to slow down when accident signs were displayed.
He said about six vehicles were forced to stop and 10 more were made to slow down.
Behaviour included rubbernecking and speeding.
Snr Const Dow said the behaviour of motorists was so bad that when the crash workers decided to lift the remains of the caravan on to a recovery vehicle, the decision was made to close both lanes to make it safe for the workers.
''[They] should be able to go about their work environment in a safe way without being put at risk.''
