Data-Driven Analysis to Support Revised Tire Tread Inspection Standards

Despite a long-term focus on passenger vehicle safety, there are still 38,000 vehicle-related fatalities annually. Some are the result of failure to maintain safety components of vehicles, such as brakes, tires, or headlights. Following NHTSA guidelines, 18 states have implemented periodic safety inspection programs in which certified inspectors assess components, and owners are required to repair or replace deficient components. In the case of tires, when the tread depth falls to 2/32 in., its stopping distance becomes excessive. Thus, this tread depth level was built into the safety inspection thresholds for tires. One challenge is that, in an annual vehicle inspection, if a tire passes at a level of 3/32 in., it may fall below the safe (2/32 in.) threshold soon after inspection. In an era of higher vehicle miles traveled (VMT) and reduced attention to maintenance, perhaps the thresholds set for safety inspections should be higher than the “safe level” to provide a buffer. Using 6 million safety inspection records from Pennsylvania from 2006 to 2016 we calculated tread depth deterioration and annual VMT at the vehicle level. We estimated the “percent of vehicles at risk of having unsafe tires before the next inspection” (using the 2/32 in. threshold) to be about 30%. We also estimated how the percent of at-risk vehicles decreases as the inspection thresholds are raised, and found an attractive threshold at about 5/32 in. for which the percent of at-risk vehicles would be very low. Such changes could further reduce fatal and non-fatal accidents.