Use of braking systems in four passenger vehicles was evaluated during a 7300 mile trip across the United States. This paper presents an analysis of braking system temperatures and torques and vehicle speeds and decelerations that were measured during the trip. Similar measurements made during SAE fade and recovery tests are also presented and a comparison of severity levels is given. Requirements for specifying braking system performance at temperatures higher than those currently considered are discussed. The need for a new test to insure that vehicles will perform satisfactorily in service with approved brake fluids is shown.