Monash university accident research centre report documentation page

5.4 Analysis of compliance data

Analysis estimated the rate of issuance of each of these warnings and notices per inspection undertaken by age of vehicle and taxi and hire car type. Over 80% of inspections were of metropolitan taxis and a correspondingly high proportion of warnings and notices also related to these vehicles. In order to undertake meaningful analysis of the data, all non-metropolitan taxis were grouped together for analysis (labelled as non-metro taxis in the figures) and compared to the data on metropolitan taxis. Figures 5.10, 5.11, 5.12 and 5.13 show the rate of rectification notices, official warnings, notices of un-roadworthiness and infringement notices respectively per inspection by age of vehicle.

Figure 5.10 shows a clear increase in the rate of rectifications per vehicle inspection for all taxi types with the trends and absolute rates being similar for metro taxis and all other taxis and hire cars. Over the life of the vehicle the rectification rate per inspection increases nearly three-fold most likely related to wear and tear on the vehicle as it ages.

Similar trends are seen in the rates of un-roadworthiness shown in Figure 5.12 although the rates of un-roadworthiness are much lower than the rates of defects with only around 5% of vehicles inspected found to be un-roadworthy on average. Although the inspection regime often targets inspections so the data may not be representative of the broader fleet, the trend to increasing rate with age still suggests vehicle deterioration. The other notable feature is the rates of un-roadworthiness drop off dramatically after seven to eight years where the inspections will largely relate to WATs and modified or high luxury hire cars. This suggests that although these specialist vehicles record defects, they appear to be less serious and therefore rarely leading to an un-roadworthy condition implying reasonably good maintenance of these vehicles with higher allowable age limits.

Of the measures examined, defects and un-roadworthiness are the ones that are most likely to be related to poorer vehicle safety and in particular crashes caused by vehicle defects. Official warnings and infringements are generally issued for non-vehicle safety related issues such as operating a taxi without a permit or refusing to take a passenger. Comparing the rates of defects and un-roadworthiness by vehicle age to trends in crash risk be vehicle age show little correlation. There is no marked trend towards increasing crash risk with vehicle age seen in the vehicle condition trends. The observed lack of association suggests that although vehicle condition deteriorates with time, the inspection regime is effective in identifying the defects before they lead to crashes and that they are subsequently rectified. Another possibility is that vehicle defects have a relatively minor role to play in crash causation which has been found in previous studies (van Schoor et al, 2001). A combination of both these possibilities is likely although the observed trend to increasing vehicle defects with age gives some support to the need for random and targeted inspection of taxis for defects and roadworthiness.

The continuous increasing trend in defects implies that if age limits of taxis were increased, and this resulted in less frequent regeneration of the fleet, the need for the compliance regime would become greater as the rate of vehicle defects continued to increase.

There are no discernible trends in the other compliance based methods examined. The rates of official warnings per inspection shown in Figure 5.11 are very low and have no trend with vehicle age. Rates of infringements are also very low and show no consistent trends with vehicle age.