A head-on collision between a Nissan vehicle and a Mitsubishi resulted from the Nissan driver's reaction to seeing what she thought was a poisonous spider in her car.

Caitlin Jade Ryan (23), medical imaging technologist, of Dunedin, was before the Dunedin District Court having admitted three charges of careless driving causing injury.

The police summary said Ryan, driving on State Highway 1, near St Andrews, about 11.40am on April 25, allowed her vehicle to drift into the oncoming lane in front of a Kenworth truck.

Ryan returned to the correct side of the road before swerving back to the incorrect side, colliding with the side of the Kenworth.

Her vehicle bounced back to the correct side before again swerving into the way of oncoming traffic and scraping the rear panel of an oncoming Ford.

It then collided head-on with an oncoming Mitsubishi.

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The driver of the Mitsubishi sustained a broken right wrist and a broken rib.

The Mitsubishi's front passenger sustained a cut spleen, an injured bowel and a bruised sternum.

The Mitsubishi's back-seat passenger sustained three cracked ribs, a cracked vertebra at the base of her neck and a cracked sternum.

Counsel Deborah Henderson applied for Ryan to be discharged without conviction.

Ryan had not previously been before the court. She was logged in for a defensive driving course and had put together a plan to deal with reparation, Mrs Henderson said. Although restorative justice did not go ahead, Ryan had been willing to attend.

Ryan had left Dunedin heading for Christchurch on the day. Her memories of the day were disjointed. She could remember driving through St Andrews and, soon after, seeing what she thought was a white-tailed spider in the car. It spooked her. Ryan could recall reaching for the button to put the window down, but not much after that, Mrs Henderson said.

Community magistrate Simon Heale granted the discharge application. But he disqualified Ryan from driving for six months (from November 1 when her defensive driving course ends) and ordered she pay reparation and emotional harm reparation to a total of $1451.50.

Matters taken into account by the magistrate in discharging Ryan without conviction included the effect of conviction on her employment and further study, and her continued professional registration and travel.