From CDC Vital Signs
Motor vehicle crashes are the leading cause of death for people age 5 – 34. Adult seat belt use is the single most effective way to save lives and reduce injuries in crashes. The percentage of adults who always wear seat belts increased from 80% to 85% between 2002 and 2008. Even so, 1 in 7 adults do not wear a seat belt on every trip. Primary enforcement seat belt laws make a big difference in getting more people to buckle up.* In 2010, 19 states--where 1 in 4 adult Americans live--did not have a primary law.
* A primary enforcement seat belt law means a police officer can pull someone over and issue a ticket to the driver just because someone in the vehicle is not wearing a seat belt. A secondary enforcement law allows a police officer to issue a ticket for someone not wearing a seat belt only if the driver has been pulled over for some other offense.