Research into driver fatigue that federal authorities recently added to the hours of service docket is faulty and should not be used to make policy changes to the hours rule, the American Trucking Associations charged.

The National Industrial Traffic League also said the studies are flawed and do not support conclusions by the Federal Motor Carrier Safety Administration.

FMCSA last month cited four studies that generally indicate that safety risk increases as work and driving time increases. They are among arguments the agency is using to try to change current HOS rules.

But two of the studies, one by Penn State and the other by the Virginia Tech Transportation Institute, are flawed in their methodology and conclusions, ATA said Wednesday in a letter to FMCSA Administrator Anne Ferro.

The association's analysis is based on several papers prepared for ATA by Ronald Knipling, a leading truck safety researcher who has worked at both VTTI and FMCSA.

In one paper Knipling explained the importance of distinguishing types of crash causes when analyzing truck safety. He said the Large Truck Crash Causation Study shows that a single-vehicle truck crash is much more likely to be caused by an impairment such as fatigue, or bad behavior, than a crash involving another vehicle.

This paper emphasizes "the acute need to disaggregate crash data in order to understand crash cause and make appropriate policy decisions," ATA's letter said. "Neither the Penn State nor the VTTI study FMCSA recently placed in the hours of service docket do so."

Knipling faulted the methodology of the Penn State study and said, "It would be erroneous and unwarranted to accept Penn State's principal findings and conclusions without extensive re-analysis, internal validation, and external replication."

The VTTI study contains a treasure trove of data but is based on narrow hypotheses, and needs more analysis before its conclusions can be accepted as sound science, he said.

Knipling's research "underscores how weak FMCSA's case for (HOS) change really is," ATA President Bill Graves said in a statement. "We have said from the beginning that changes to the rule must be made based on sound science and hard evidence, not political motivations.

"FMCSA should abandon its ill-advised proposal and turn its focus to improving enforcement of the current, effective hours-of-service rule."

The National Industrial Traffic League, representing member shippers, said in its comments that the feds' studies are not persuasive.

The Penn State study implies that fatigue caused the crash risk and that the risk increased with each driving hour, but it makes no attempt to verify that the crashes were caused by fatigue, the NIT League said.

And the VTTI study does not validate the conclusions that increased crash risk over a 14-hour duty period or after a rest period is a matter of driver fatigue.

"The study shows no appreciable increase in crash risk between the 10th and 11th driving hours, which would support a change to the current rule," the League said.

FMCSA has pushed back the scheduled date for completion of the hours of service revision. Originally it was to done next month but now the agency says it will publish the final rule by October 28.