WASHINGTON—For the third time in three years, portions of the hours-of–service (HOS) rules, governing an estimated 8 million truck drivers, have been ruled illegal.

A federal court threw out the latest truck driver HOS regulations, ruling that the Federal Motor Carrier Safety Administration (FMCSA) violated procedural law when it crafted the rules. As a result, shippers and carriers are scrambling yet again to calculate the ruling’s effects.

Mark Rourke, president of the truckload division of Schneider National, said the ruling has yet to cause any immediate problems, but he was “disappointed” by the news. “It seems more procedural than content,” said Rourke. “We’re confident the industry can get it remedied, but the uncertainly is unsettling.”

The unanimous July 24 ruling, made by a three-judge panel of the U.S. Court of Appeals in Washington, overturned the 11-hour daily driving limit and 34-hour restart period that have been in place since the current rules took effect Oct. 1, 2005. That resets the HOS clock at 10 hours maximum driving time each day. In the 39-page opinion, Judge Merrick Garland called the rule “arbitrary and capricious.”

The American Trucking Associations (ATA), which backed the original rules, issued a sunny statement saying, “From the trucking industry’s standpoint, the good news in the decision is that the flaws that the Court found were procedural in nature and can be corrected by the agency.”

The ATA said it will seek a stay of the ruling, which is scheduled to go into effect in mid-September. The FMCSA stated that it is studying the ruling and has not indicated whether it would appeal.

Satish Jindel, principal of SJ Consulting, called the ruling a “double-edged sword” for truckload (TL) carriers. On one hand, he said, it would result in reduced capacity of about four to five percent and lower productivity for TL carriers. But the ruling comes at a time when the industry currently has excess capacity due to the freight slowdown.

Nevertheless, shippers are concerned that the ruling will create uncertainty in the market place. Fred Boehler, vice president of logistics for Borders Group, a major truck shipper, said he’s confident the truckers will adapt to whatever final rule is adopted. “The question is how will they react,” said Boehler.

Ed Wolfe, trucking analyst for Bear Stearns, said in a note to investors that large TL carriers would be hurt by the scaled-back driver hours. He noted that back in 2004, when the rules first went into effect, capacity was tight and the TL carriers were able to charge accessorial fees and detention fees to offset the costs of compliance. Now, with more available capacity in the market, Wolfe said, it may be more difficult to offset the negative impact to capacity.

Schneider’s Rourke said the exact impact of the original ruling was about a five to six percent reduction in productivity. But he said from a safety aspect, he believed the original rule was working as intended. “Our safety record has never been better,” Rourke said. “It absolutely has played out as intended: a reduction in accidents.”

Other safety advocates and others hailed the ruling as a victory.

“The court has once again sided with public safety and rejected FMCSA’s illogical proposition that driving longer hours and working longer days will somehow solve truck driver fatigue,” said Judith L. Stone, president of Advocates for Highway and Auto Safety, which challenged the 2005 rule.

Others agreed. “We never thought it was a good idea to allow drivers 11 hours behind the wheel of a heavy piece of machinery,” Teamsters union president Jim Hoffa said. “I hope this ruling forces the Bush administration to start paying attention to highway safety.”