State decisions to raise speed limits have cost 33,000 lives in the U.S. over two decades, according to a new study from the Insurance Institute for Highway Safety.

In 2013 alone, speed limit increases resulted in 1,900 more road deaths, IIHS research found. That increase basically canceled out the number of lives saved by frontal air bags that same year.

“Although fatality rates fell during the study period, they would have been much lower if not for states’ decisions to raise speed limits,” said Charles Farmer, IIHS vice president for research and statistical services and the author of the study.

The study examined the effect of all speed limit increases in 41 states from 1993 to 2013. Not included were increases of the past three years. The District of Columbia and nine states were excluded because they had relatively few vehicle miles traveled each year, resulting in wide swings in their annual fatal crash rates.

To reach his conclusions, Farmer looked at deaths per billion miles traveled by state and roadway type. He also took into account other factors affecting the fatality rate, including changes in unemployment, the number of potential young drivers (ages 16-24) and per capital alcohol consumption. Ultimately, he determined that each 5 mph increase in the maximum speed limit resulted in a 4% increase in fatalities. On interstates and freeways, the increase was 8%.

Farmer compared the annual number of fatalities in the 41 states against the expected numbers had each state’s maximum speed limit remained unchanged since 1993. This calculation brought him to the estimate of 33,000 additional fatalities over the 20-year period.

The total of 33,000 is likely an underestimate, Farmer said, because he considered only increases in the maximum speed limit, which often applies to rural interstates only. Many states also increased speed limits on urban interstates.

Additionally, some states raised speed limits on one section of road and subsequently extended the higher limit to other sections. Those changes weren’t factored in, either.

Speed limits have continued to climb since the end of the 20-year period covered by the study. Six states now have 80 mph limits. Some roads in Texas even permit driving at 85 mph.

"Since 2013, speeds have only become more extreme, and the trend shows no sign of abating,” Farmer said. “We hope state lawmakers will keep in mind the deadly consequences of higher speeds when they consider raising limits.”

To download the study, click here.

In response to the study’s conclusions, the Governors Highway Safety Association issued a statement urging states and communities to stop raising speed limits. Instead, GHSA encouraged strong enforcement of existing speed limits, both through policing and judicious use of speed cameras.

“We know that crashes are more deadly as speeds increase,” GHSA said. “In addition, most drivers treat maximum speeds as a minimum target. Past research has shown that as posted speed limits are raised, drivers will exceed these limits, and more fatal crashes will result. This new research reinforces earlier studies and provides clear evidence of the negative safety implications from increasing speed limits.”

The National Safety Council released a statement as well.

“The National Safety Council strongly urges states, cities and municipalities to study this report and its implications on current speed limits, and to prioritize the adoption and use of speed cameras and automated enforcement, which has been proven to save lives, while ramping up traditional enforcement tactics," the organization said.