More than 9,000 deaths — 28 percent of all crash fatalities — occurred in speed-related crashes in 2014. High speeds make a crash more likely because it takes longer to stop or slow down. They also make collisions more deadly because crash energy increases exponentially as speeds go up.

Raising speed limits leads to more deaths. People often drive faster than the speed limit, and if the limit is raised they will go faster still. Research shows that when speed limits are raised, speeds go up, as do fatal crashes.

Enforcement of speed limits helps keep speeds down. Traditional enforcement, which relies on police officers to measure speed with radar or other technology, has been joined recently by speed cameras. Speed cameras, which are used in more than 100 U.S. communities, have been shown to reduce speeds and crashes.

Speed cameras across the U.S.

Find out which communities operate speed camera programs and get information on state laws governing automated enforcement.

Video: Automated enforcement