Under section 13 of the Transportation Recall Enhancement, Accountability, and Documentation (TREAD) Act, the Secretary of Transportation was required to complete a rulemaking for a regulation mandating a warning system in each new motor vehicle to indicate to the operator when a tire is significantly under-inflated. Accordingly, the accompanying final rule requires a tire pressure monitoring system (TPMS) to be installed in all new passenger cars, multipurpose passenger vehicles, trucks, and buses that have a gross vehicle weight rating (GVWR) of 4,536 kg (10,000 lbs.) or less, except those vehicles with dual wheels on an axle. The final rule requires that the driver be given a warning when tire pressure is 25 percent or more below the vehicle manufacturer's recommended cold tire inflation pressure (placard pressure) for one to four tires. (We note that the agency had previously issued a final rule providing two different compliance options with different levels of stringency. However, a court decision1 found that the TREAD Act requires a TPMS with a four-tire detection capability, so the court vacated the standard for further rulemaking consistent with its opinion.) The final rule also requires a TPMS malfunction indicator, as well as a warning when the system detects under-inflation of 25 percent or more in one to four tires. For this Final Regulatory Impact Analysis, the agency estimated the impacts of three TPMS systems that the manufacturers could use to meet the final rule. Compliance Option 1 assumes that manufacturers will supply a direct system with a warning lamp and either an interactive or continuous readout of individual tire pressures. Compliance Option 2 assumes that manufacturers will supply a direct system with a warning lamp. Compliance Option 3 assumes that manufacturers with an ABS system would use a hybrid measurement system (indirect system with two direct tire pressure measurements) and vehicles without ABS would use a direct measurement system. We assume a warning lamp will be provided for drivers.