A safety group has gone to court against the agency, calling the rule too lax, while the trucking industry has filed a suit calling it too strict. And both sides point to the same data to back their claims.

It’s a hugely important issue — truck crashes kill thousands of people each year, with most deaths occurring in the vehicle that collided with the truck. The agency enacted the new requirements after years of work and public outcry from safety groups, making the first changes to the rule since 2004. The revisions are set to take effect in July 2013.

At the center of the debate is a 55-page edict guided by scientific data on sleep and driver fatigue that quickly becomes complicated and open to interpretation.

Perhaps the most crucial part of the new rule is language limiting the number of consecutive hours truckers can drive. The final rule that came back from the Office of Management and Budget kept the previous 11-hour cap, even though FMCSA had been considering dropping it to 10.

The American Trucking Associations, which has sued to stop the rule, calls the industry safer than ever. It says the sleep data and the rule’s supposed economic benefits provide shaky foundations for tougher requirements.

The FMCSA “admits in its analyses that purely from the standpoint of safety, the costs of these rules will outweigh the benefits — and several critiques of FMCSA’s work found even those benefits were overstated,” ATA spokesman Sean McNally said. “In order to satisfy regulatory requirements, FMCSA was forced to rely on what several researchers have said is unproven research into the alleged health benefits of these changes.”

Meanwhile, safety advocates also raise questions about the data.

“They now have said they don’t know if the 11th hour is safer or not as safe as the 10th hour,” said Henry Jasny, vice president and general counsel for Advocates for Highway and Auto Safety. “They’ve always admitted that it’s at least as unsafe, that it may be more unsafe, but they don’t have the data so they’re not going to change it.”

If FMCSA won’t cap driving at 10 hours now, Jasny wonders why the limit was boosted from 10 to 11 in 2004. “If they don’t have the data now, they didn’t have it back then, so our argument still has life that the agency is working in the dark and what happened back in 2004 shouldn’t have happened.”

The Department of Transportation stands by the rule and maintains it will improve what Secretary Ray LaHood frequently calls the agency’s top mission: safety.

But not everybody sees it that way, casting doubt on the old Washington saying that if a policy change upsets everyone, it’s the right thing to do.

“The theory that a good rule is one in which all sides are unhappy is not true, it really isn’t,” House Oversight and Government Reform Committee Chairman Darrell Issa (R-Calif.) told POLITICO. “A good rule is one in which the public is protected, that the narrowest use of authority yields the greatest benefit.”

Issa’s committee looked into the rule in a hearing in November, nearly a month before the final rule was unveiled. Republicans and trucking industry witnesses spoke against the potential 10-hour cap, saying it would mean more trucks on the road and higher shipping costs.

Even though the final rule kept the 11-hour limit, Issa is upset by a different provision: the “restart” that lets a trucker rest for 34 hours and begin a new workweek. The new rule requires two straight days of breaks from 1 a.m. to 5 a.m. and lets the driver restart only once a week. Those are new restrictions — drivers used to be able to restart midweek and potentially serve two full workweeks in just over a week.

“Clearly what they did is a rule that indirectly or comparatively favors unions because of the whole start-time issue,” Issa said, saying the restrictions will mean more trucks — and therefore truckers — on the road. “It seemed like they missed it a little bit.”

The new restart provisions just don’t target a large enough pool of drivers, Jasny said. On top of that, lots of trucks will be hitting the road around 6 a.m. — just in time to catch the morning rush hour. That doesn’t make sense to Jasny.

“The limitation they put on it affects a bunch of drivers, but those on shorter, more local schedules who tend to be home sleeping at night, not the drivers that we’re most concerned about,” he said.

He also questioned the delay until July 2013 for the rule to kick in. “If they thought this was a very important safety change, why would you wait 18 months to implement it?”

Both sides expect a court resolution before the rule takes effect.

Issa said tired truckers are only one of many safety concerns on the road.

“To be honest, Breathalyzers, testing for alcohol, would do more than anything else in all driving,” he said. “Distracted driving, Secretary LaHood’s No. 1 agenda: huge because truckers are no different than anybody else. So when we look at the safety of trucks on the road, tired is definitely a factor, and we want to address it with the maximum benefit for the minimum drop-off in efficiency.”

ATA also sees other factors that have a bigger impact of safety. One is a rule, struck down by a court, that would have required electronic on-board recorders on trucks with the worst safety records. The group has filed a friend-of-the-court brief supporting that idea.

Under the current setup, enforcement of the hours-of-service rules largely relies on paper logbooks that can be easily manipulated. It’s a separate issue in the courts but is something that has brought ATA and the safety advocates together. Owner-operators, after having it struck down, remain opposed to the rule.

Opposition to the electronic records rule is part of “a war against 20th-century technology, let alone 21st-century technology,” Jasny said.