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Expert witness requested to redo calculations

Expert witness requested to redo calculations

THE methods and formulas used by the motor vehicle reconstruction expert to make calculations and other niggling discrepancies in the report commissioned by the Hollard insurance company came under severe fire from the defence counsel of Jandré Dippnaar during the fourth day of the murder trial in the Swakopmund Regional Court.

For the past two days under cross examination, Mr. Johan Joubert, managing director of Traffic Accident Reconstruction Services in Cape Town South Africa, had a hard time explaining how he reached the conclusions as certain technical details of his report were scrutinised by Advocate Louis Botes.

It was put to the witness that he relied on a speed reading derived from the Global Positioning System (GPS) device used in tracking self drive tourist vehicles in Namibia to do some of the calculations.

The speed of 85 kilometres per hour at which the late Walter Helmut Joschko drove when the gruesome crash occurred about 12 kilometres south of Henties Bay on 29 December 2014 was provided to Joubert by the vehicle rental company.

Advocate Botes put it to the witness that his entire report is based on the pre-impact velocity provided from a third party and that it boils down to hearsay evidence.

Joubert was also asked to use a different formula to the one he used to redo his calculations while the court stood down for an hour on Thursday. When court proceedings resumed Joubert had to admit the values obtained from the use of a different formula to calculate the momentum of the Toyota FJ Cruiser and the Ford Ranger differed slightly from his.

He stated that the change in certain values derived from the new calculations had little or no effect on the final result. He stated that the differences are negligible and would still lead to conclusions very similar to his own.

When the document containing the new calculations was handed up as an exhibit, Joubert asked that it should be marked as provisional because the expert witness for the defence still has to testify on it.

The cross examination also bogged down on the differences between friction coefficients and drag coefficient and how it was derived from an analysis of the accident scene.

Joubert was asked why he only used a Ford Ranger similar to the one driven by Joschko on the fateful day to determine braking distances and not a JFJ Cruiser as well. He said he only had the pre-impact velocity of the Ford and had to test the only known value available as a baseline to determine the rest of the values and angles contained in his report.

The quality of Joubert’s work also came under fire because certain pictures denoted the time to be at 23:00 at night while they were clearly taken during daytime. GPS coordinates noted on one of the pictures in his photo plan put the position of the picture approximately 14 kilometres away from the actual accident scene.

The cross examination of the accident reconstruction expert is set to continue tomorrow.

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