Samenvatting
Safety belt use was shown to increase in urban areas by the introduction of the interlock system in 1974 vehicles. At least a lap belt was in use twice as frequently in 1974 vehicles equipped with the interlock system as in 1973 vehicles equipped with the buzzer-light system observed under the same conditions; but 41% of the 1974 vehicle-drivers were not using any belts. A large difference among usage rates in vehicles produced by different manufacturers is noted. Smaller or nonexistent differences in belt usage were found between racial, sex, and age groupings.