Evaluations of the effectiveness of primary laws have consistently shown noteworthy benefits. A systematic review of evidence by the Centers for Disease Control and Prevention examined 13 studies and reported that primary laws increase use by an average of 14 percentage points and reduce occupant fatalities by 8 percent compared to secondary laws.26 Appendix F, which provides a summary of safety belt use rates by law type, illustrates the increased safety belt usage in primary law States.
The following are some impressive examples of the effectiveness of primary enforcement laws in raising safety belt use:
Tennessee: Safety belt use rates rose from 68.5 percent in 2003 to 72 percent in 2004, after Tennessee passed its primary law. In 2005, the rate was 74.4 percent.
Illinois: The safety belt use rate in Illinois rose from 74 percent in 2002 to 80 percent in 2003, after passage of a primary law.
Oklahoma: When Oklahoma upgraded its belt law to primary enforcement in 1997, the usage rate increased from 48 percent (1996) to 68 percent in 2001, an increase of 20 percentage points. In 2005, the rate was 83.1 percent.
New Jersey: When New Jersey introduced its primary enforcement safety belt use law in 2000, its usage rate climbed from 63 percent in 1999 to 74 percent in 2000. In 2005, New Jersey’s safety belt use rate rose to 86 percent.
Michigan: In 1999, the safety belt use rate in Michigan was 70 percent. After Michigan upgraded its belt law to primary enforcement, the safety belt use rate in 2000 climbed to 84 percent—a 14-percentage-point increase, and reached 93 percent in 2005.
Alabama: After the introduction of its primary enforcement safety belt use law, Alabama’s safety belt usage rate rose dramatically from 58 percent in 1999 to 79 percent in 2001. In 2005, the rate was 82 percent.