Results are presented of a study of tire disablements and accidents on a toll road. The study was made on a toll road for the following reasons: (1) toll collections give a very precise measurement of vehicle mileage, (2) continuous high speed is acknowledged to be severe on tire service and increases accident severity, (3) accidents are more completely reported on a toll road, and (4) uniform speeds minimize speed as a variable in the study. Only four-tired vehicles were included in the study, mainly, passenger cars. Three surveys were conducted which gave disablement rates for three temperature-trip lengths combinations. Disablements per mean car miles varied from 29 for low temperature and long trips to 71 for high temperature and short trips. a condition survey was conducted on 1746 four- tired vehicles in the parking areas of five service centers. Among the 1746 cars surveyed, there were 1022 ailing tires. This would average 0.59 ailing tire per car. For the 12 months of the study, patrolmen on the tollway were requested to make a specail report when they encountered a car stopped on the roadside with a disabled tire. The report included the same data collected in the condition survey, except that the load on tires and air pressure in the disabled tire could not be measured. Comparing tread wear of disabled tires with those in general use permitted calculation of disablement indexes for various remaining tread depths. It was found that the disablement curve rises sharply after wear reduces groove depth to less than 2/32 inch. This fact supports 2/32 in. As an inspection standard requirement. Bald tires appear to be about 45 times as susceptible to disablement as new tires. Police made reports on tire disablements followed by accidents. These data were compared with the survey of disablement not followed by accidents and the condition survey. During the 12 months not more than 36 accidents followed tire disablements. Risk indexes were computed by age and sex for drivers of cars experiencing accidents following disablements. Study results indicate that people who pay to use a toll road are likely to afford better tires than other car owners. High speeds, however, are more likely to cause disablements and make coping with them more difficult. (Author/publisher)
Samenvatting