Although previous research has identified some safety benefits accruing from periodic vehicle inspection programmes, such benefits may not be sufficient to justify the costs of such schemes. This study conducted analysis of merged crash and licensing data from two jurisdictions, Victoria and New Zealand, where periodic vehicle inspections are conducted to certify roadworthiness at the point of sale of a vehicle (Victoria and New Zealand) or at 12-montly or 6-monthly intervals (just in New Zealand).

New Zealand crash data, licensing data and inspection data from the warrant of fitness (WoF) scheme were merged together to evaluate the safety benefits in terms of reduced crash risk and the reductions in safety- related vehicle faults associated with the increase from annual to biannual inspections that occur six years after the car’s manufacture date. These were estimated to be respectively 8% (with 95% confidence interval 15% to 0.4%) and 13.5% (with 95% CI 12.8%-14.2%). The proportion of vehicle faults prevented is likely to be at least maintained over the vehicle age range 7-20 years, suggesting that the resultant safety benefits should also be maintained. The confidence interval for the drop in crash rate was wide, showing considerable statistical uncertainty about the precise size of the drop although indicating the likely drop is less than 15%. Despite these safety benefits, the costs to the motorist of the 6-monthly inspections over and above the annual inspections were estimated to be considerable, valued at $250 million annually, excuding the overall costs of administering the scheme. This means that the 6-monthly inspections are very unlikely to be cost-effective. The WoF scheme as a whole cannot be robustly evaluated using the analysis approach used here, but the safety benefits would need to be substantial – yielding at least a 12% reduction in injury crashes – for it to be cost-effective.

The Victorian analysis of potential periodic roadwothiness certification safety benefits was not entirely conclusive. It suggested the maximum annual crash savings associated with moving to annual vehicle roadworthiness inspections for vehicles over 5 years old to be around 4%, which is likely to be much less than required to make an annual periodic scheme cost effective.

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