This report is an analysis of the data collected through the Tire Pressure Monitoring System-Special Study as it pertains to the effectiveness of TPMS in promoting proper tire inflation. The study was conducted in 2011, using a nationally representative sampling structure, based on the primary sampling units (PSUs) of the National Automotive Sampling System. NASS personnel collected 6,103 complete vehicle observations including tire pressure of all four tires. Proper tire inflation is important for several reasons. Underinflated tires experience a greater amount of sidewall flexion than properly inflated tires, resulting in decreased fuel economy, sluggish handling, longer stopping distances, increased stress to tire components, and heat buildup that can lead to catastrophic failure of the tire, such as cracking, component separation, or blowout. These catastrophic failures can cause loss of vehicle control and may result in a crash. Overinflated tires may be more easily damaged by potholes or debris. Severe overinflation may increase stopping distance due to reduced area of road contact and non-optimal traction, and may also contribute to vehicle instability. As with underinflation, overinflation may result in uneven tread wear that reduces the useful life of the tire. This report does not attempt to directly measure the relationship between TPMS and vehicle safety; rather it measures the relationship between TPMS and proper tire inflation. In order to estimate the effect that TPMS has on crash avoidance and mitigation, future analyses are planned that will use real world crash data. Sivinski, R. (2012, November). Evaluation of the effectiveness of TPMS in proper tire pressure maintenance. (Report No. DOT HS 811 681). Washington, DC: National Highway Traffic Safety Administration.