In the context of regulating truck weight limits, the concept of performance-based standards (PBS) may be applied to three areas--infrastructure, traffic operations, and safety. Using a certification as documentation of vehicle compliance with a PBS has been suggested as an option for PBS enforcement. Enforcement is essential in encouraging voluntary compliance with laws or regulations governing vehicle weight and operation. The traditional method of vehicle weight enforcement is to use static, portable, or semiportable scales to determine the axle or gross weight of a vehicle. Any proposal to use a certification as documentation of PBS compliance for truck size and weight limits must be examined closely for enforceability. Maryland's use of a certification for enforcement of a lift-axle weight regulation is examined from an enforcement perspective, and the process used to develop the regulations is discussed. Enforcement of the lift-axle weight limit is based on the air pressure setting, not on weighing the axle with a scale. The certification is important because it documents the air pressure setting required of the lift-axle on a loaded, four-axle dump truck at 31,780 kg (70,000 lb). This study represents the first external review of issues identified in using the certification, and the enforcement experience since implementation.