Laurie Beck, a researcher at the Centers for Disease Control and Prevention in Atlanta, said 87 percent of U.S. adults use seat belts.
"Although most people now wear seat belts, there are still millions of people who are taking unnecessary risks by traveling unrestrained," Beck said in a statement.
Beck said people who live in rural areas, men, teens, young adults and nighttime travelers are less likely than others to buckle up.
Beck said seat belts are the most effective protection drivers and passengers have in crashes, and cut the risk of serious injury or death by about half.
Seat belts are mandatory except in all U.S. states except New Hampshire. In some states, laws cover front-seat occupants only, while seat belt laws in 28 states and the District of Columbia cover rear-seat occupants, too.