The role of critical incidence and prevalence studies in truck safety research.

Descriptions of a number of heavy truck inspection and observation studies recently performed in several regions of the United States are presented.These studies were done to establish the relative prevalence of various aspects of heavy truck operation and in- use condition. / Results of these "prevalence" studies are presented. They involve heavy truck front brake operability, speed control practices on downgrades and in curves and the prevalence of various safety- related equipment features.