WASHINGTON -- A U.S. government study has concluded that there is no significant link between retreads and accident-causing debris on the road.

The National Highway Traffic Safety Administration recently issued its final report on its Commercial Medium Truck Tire Debris Study, which examined hundreds of discarded tire casings from truckstops and over 1,000 tire fragments that were collected along the interstate highway system at five representative locations throughout the U.S.

The casings and tire fragments were examined by tire forensic experts to determine the probable failure type, axle location of the failed tire, and the likely reason for the tire failure.

Among other findings, the analysis concluded that the proportion of tire debris from retread tires and OE tires is similar to the estimated proportion of retread and OE tires in service.

"Indeed, the OE versus retread proportions of the collected tire debris broadly correlated with accepted industry expectations," states the report. "Additionally, there was no evidence to suggest that the proportion of tire fragments/shreds from retread tires was overrepresented in the debris items collected."

Examination of tire fragments and tire casings (where the OE or retread status was known) found that road hazard was the most common cause of tire failure, at 38 percent and 36 percent respectively. Maintenance and operational issues accounted for 32 percent of the failures while over-defection accounted for 16 percent. Analysis found that excessive heat was evident in 30 percent of the samples.

"These results suggest that the majority of tire debris found on the nation’s highways is not a result of manufacturing-/process deficiencies."

Furthermore, whether a tire is mobile or stationary, maintaining the correct tire air pressure is the key to optimal tire performance, safety, and durability, the study found.

The Tire Retread Information Bureau (TRIB) hailed the study as evidence of what it has said all along -- contrary to popular belief, retreads are not the cause of "rubber on the road."

The industry group has been busy battling several jurisdictions in North America that have considered banning or restricting retread tires.

(Incidentally, NHTSA says that despite "strenuous efforts by the principal investigator" to incorporate input from an advocacy group or institution championing a prohibition of retreads, none was forthcoming.)

"The study contains a huge amount of important information about the true causes of tire debris, but it makes clear that retreads are not to blame!" TRIB said in a press release.

As for the rate of failed tire debris directly causing a crash of the same vehicle or following vehicles, that question is more of a challenge to assess because of the lack of available data, states the NHTSA.

However, the agency explains how a "variable in the Fatality Analysis Reporting System (FARS)" dataset can be used to infer a fatal crash resulting from debris in the road, "although tire debris per se is not explicitly defined in this variable."

Thus, roadside debris in this case must be taken in its widest sense, to include fallen trees, lost cargo, tire debris, etc.

In that sense, the study determined that vehicle crashes related to truck tire failure and truck tire debris are very rare events "that account for less than 1 percent of traffic crash involvements."