Braking Capability Requirements for In-Use Commercial Vehicles - A Chronology

Abstract

Manufacturers of new commercial vehicles (CVs) sold in the U.S. must certify that the vehicle meets safety standards for braking capability via stopping performance tests (FMVSS 121). However, for the remaining 10- to 20-year service life of that CV, the carrier is responsible for ensuring that it is maintained in safe operating condition, under regulations codified in 49 CFR 393 and 396. The origin of these Federal Motor Carrier Safety Regulations (FMCSRs) for braking safety of in-use vehicles can be traced back to 1936, with the first publication of stopping performance requirements. However, due to the logistic challenges of conducting stopping performance tests, such tests are seldom performed on in-use vehicles. As such, research was conducted in the 1950s through the 1980s to find an equivalent method, via inspection of brake system components, to that of the performance-based regulations for identifying vehicles that were considered unsafe for travel on the public roadways. Modern performance-based brake test equipment provides an alternate method to both stopping tests and visual inspections to determine the braking capability of in-use vehicles. Although relation of these measurements to stopping performance requires additional information, identification of under-braked in-use vehicles is directly possible. This paper provides a historical chronology of CV braking performance and requirements, and a look at the evolution and future of CV brake systems and brake performance assessment.