This article describes a test program conducted by the National Highway Traffic Safety Administration to assess the performance of commercial vehicle stability control (SC) systems under controlled conditions on a test track. The performances of three tractors equipped with trailer-based electronic stability control (ESC), one semitrailer equipped with either ESC or roll stability control (RSC), and three motorcoaches equipped with ESC were evaluated, along with six baseline semitrailers wihtout an SC system. Testing was conducted in three phases; the focus of this article is the third phase, in which a dynamic test maneuver was developed to challenge tractor semitrailer's yaw stability.