The Institute for Road Safety Research SWOV carried out an inspection of the tyres of approximately 6000 cars in the Netherlands during November 1976 in order to measure their tread-depths. The sample was taken at the parking lots of roadside restaurants, motels, and modern shopping centres and showed a slight bias in favour of newer cars. By weighting the sample a representative picture was obtained for all cars used on the roads. The weighting was carried out using data from the monthly car survey of the central bureau of statistics in the Netherlands. The percentage of cars with smooth tread tyres was much smaller than obtained by other inspections of select samples. Only 1.3 per cent of the cars had one or more tyres with a tread-depth of less than 1 mm (the legal minimum); a further 4.9 per cent had one or more tyres with a tread-depth of 1 to 1.6 mm. These percentages were slightly lower than the results which the SWOV obtained in 1974 during a comparable inspection. There are indications that the situation in 1979 hardly differs from that in 1976. Although the percentage of smooth tread tyres is small, the annual number of fatal and injury accidents in the Netherlands would decline by about 500 if all tyres with a tread-depth of less than 1.6 mm were to be replaced. The SWOV emphasizes that an insufficient tread-depth is not the only tyre aspect which threatens the safety of car occupants. Other tyre characteristics which can have a negative effect on road safety are: low tyre pressure, dried-out tyres, holes and tears, irregular wear, and combining diagonal-ply and radial-ply tyres on the same car.
Samenvatting