The agency also told a federal appeals court that the risks of the 11-hour limit on driving are outweighed by the productivity savings, and the 30-minute rest break improves safety.
The agency was responding to a petition from American Trucking Associations objecting to a change in which the 34-hour restart will be limited to once a week, with each restart including two rest periods between 1 a.m. and 5 a.m.
ATA also objects to the requirement that a driver must take a half-hour off if it's been more than eight hours since he took an off-duty or sleeper berth break.
The agency told the U.S. Court of Appeals for the District of Columbia Circuit that ATA's objection to the break requirement is based on a misreading of the scientific evidence, which shows that off-duty breaks provide the greatest safety benefit.
The agency's position on the 11-hour rule is in response to objections from the safety advocacy community, which holds that the limit should never have been increased from the former 10-hour restriction.
The agency said its analysis shows that even if there is small increased risk of more crashes associated with 11 hours of driving, the cost of the those crashes will be outweighed by the productivity savings of having the extra hour.
Final briefs in this case are due Nove. 21. Oral arguments have not been scheduled. The outcome of the case could change the effective date of the hours-of-service changes, now scheduled for next July.