The number of people killed in large-truck crashes increased for the fourth straight year, bucking a trend of overall improvement in U.S. highway safety.

Fatalities rose to 3,964 people last year, which includes truckers, pedestrians and the occupants of vehicles that collided with the big rigs, the U.S. Transportation Department said in its annual traffic-injury report. That’s up 0.5 percent from 2012, even though highway deaths involving all types of vehicles fell 3.1 percent to 32,719.

Regulators said the trend can be reversed with the help of new federal standards requiring stability-control technology to prevent rollovers and future rules that may require stronger underride guards on the backs of semi-trailers.

“We do know tired truckers are a risk on our roads,” David Friedman, the deputy administrator of the National Highway Traffic Safety Administration, said Tuesday in a telephone briefing with reporters. “Any effort to reduce the number of people who are tired or drowsy on the road can have an impact.”

The report was issued a week after Congress suspended part of a set of regulations intended to ensure that truckers get adequate rest.

Lawmakers targeted a portion of the rule closing a loophole that kept some drivers from working 82 hours over eight days, according to Transportation Secretary Anthony Foxx. That provision won’t be enforced for at least a year as regulators conduct research to see if it had an unintended effect of forcing more trucks onto the road during rush hours.

Regulators will monitor whether the new policy affects the fatality count, Foxx told reporters.

“The hours-of-service rule is a critically important rule,” Foxx said. “Critical pieces of it have now been changed.”

The overall state of highway safety is improving, Friedman said. Besides the decline in all kinds of traffic deaths in 2013, the year tied an all-time record for the lowest fatality rate—1.1 people were killed for every 100 million vehicle-miles traveled.

“The data continues to show that this is just about the safest time to travel on America’s roads,” Foxx said.