This technical report examines the accuracy of gas station air pump gauges from two angles: · variables which have an explanatory relationship with gauge accuracy are identified and both the direction and magnitude of this relationship is quantified. · the question of whether there is any relationship between the accuracy of gas station air pump gauges and the prevalence of tire under-inflation in the vehicle population is investigated. Consistent with the TREAD Act’s specification of tire under-inflation as being the most serious problem, the aspect of gauge accuracy that is examined is whether or not gauges over-report the true pressure by 4 psi or more. Gauge accuracy was found to be explained to a statistically significant degree by region, volume of traffic and pump fees. In addition, statistically significant interaction effects were identified between region and traffic, between pump fees and traffic, and between traffic and station gauges in the West. The relationship between tire pressure over-reporting by station gauges and tire under-inflation among vehicles was evaluated by comparing motorists who normally check their tires using a gauge vs. motorists who do not. The South is the only region of the country where the former group showed (as one would expect) a statistically significant advantage with respect to the fraction of vehicles having all 4 tires underinflated by 4 psi or more. Since the South has by far the smallest percentage of stations having gauges which over-report by 4 psi or more, therefore, over-reporting among station gauges appears to be related to tire under-inflation. (A)
Abstract