DETROIT – Seat belt laws that allow police to stop motorists for failing to buckle up have reduced death rates by 7 percent, according to a study released today by the insurance industry.

The Insurance Institute for Highway Safety estimated that 700 lives could be saved each year if other states tighten seat belt laws.

The study looked at primary seat belt laws, which allow police to stop motorists for failing to use belts. Secondary belt laws allow police to ticket motorists for failing to wear seat belts, but only if they were pulled over for something else.

The study looked at driver fatality rates in the District of Columbia and nine states that had secondary seat belt laws in 1989 but had enacted primary seat belt laws by 2002. It compared the states’ highway deaths from 1989 to 2003 to those of 14 other states that had secondary seat belt law in place throughout that period.

The institute found states that changed their laws had a 35 percent total reduction in deaths per vehicle miles traveled, compared to a 27 percent decrease for states with secondary belt laws. Both groups saw seat belt use rise, but states with primary laws made bigger gains.

Taking into account improved vehicle safety and other factors, the institute estimated the death rate fell 7 percent in states with primary seat belt laws because of the change.

Twenty-one states and the District of Columbia now have primary seat belt laws and 28 do not.

The states in the study that switched from secondary to primary seat belt laws are California, Georgia, Indiana, Louisiana, Maryland, Michigan, New Jersey, Oklahoma and Washington. In New Hampshire, people younger than age 18 must wear a seat belt.