"There is a high probability the car was travelling at a speed," accident specialist Craig Proctor-Parker told the Johannesburg Magistrate's Court.

He said this could have been a major cause of the accident.

Mankazana, 25, a friend of the Mandela family, was taking Zenani Mandela home after a World Cup concert at the Orlando Stadium on June 11, 2010, when he crashed on the M1 freeway. The Mercedes Benz hit a steel barrier, which penetrated the car.

Zenani, in the back seat, was killed. Mankazana and another passenger were slightly injured, but neither went to hospital.

Mankazana faces a charge of culpable homicide and another of reckless or negligent driving.

Proctor-Parker said the car's brakes were working at the time of the crash.