Research in developed countries suggests that vehicle defects cause about 3% to 5% of crashes
(WHO World report on road traffic injury prevention). It is likely that the figures are much higher in low and middle income countries as the vehicle fleet is likely to be older, and less well maintained. This is especially true of heavy vehicles which are used to move freight and passengers.
In some countries systems are in place to ensure that owners have their vehicle inspected for defects that could affect safety. Inspections might occur on a regular basis (e.g. once a year) and/or at key points in time (e.g. before the vehicle is sold to another person).
While research in developed countries has not shown that regular vehicle inspections by trained authorities reduce injury crashes (2) it is a useful tool when starting a nationwide program to improve road and vehicle safety as it removes dangerous vehicles from the road (or allows time to repair them) and makes sure that the vehicles that are on the road have a suitable level of safe roadworthiness.
Where a structured inspection program (for instance on an annual basis) is not feasible, roadside checks may also be undertaken, typically in association with enforcement agencies (Treatments\Safer People\Enforcement)
Inspections are not designed to make sure that a vehicle runs smoothly and reliably, they are designed to assess the important safety features. They do not check safety features that can be thought of as additional to the basic vehicle such as airbags or traction control. For example, the major safety features checked by authorities in Victoria, Australia include the structure of the vehicle itself, the condition of the tyres (e.g. depth of tread), that the wheels are securely attached, the engine, steering, suspension, brakes, and lights are in good working order, and that the windscreen wipers and seatbelts work (VicRoads Roadworthiness certificates).