Raising Posted Speed Limits Significantly Increases Fatal Accident Risk: AAA Study

A growing number of states nationwide are considering new legislation to raise speed limits this year, believing the changes will help improve commute times and reduce traffic volume on U.S. roadways. However, new research suggests that the measures are unlikely to achieve those goals, and may significantly increase the risk of fatal car accidents.

In a study published last week, researchers with the AAA Foundation for Traffic Safety (AAA Foundation) found raising the speed limit five mile per hour (mph) led to an increase in car accident related deaths, injuries, and property damage. They also found changing the speed limit did not affect traffic volume or travel times in any substantial way.

The findings align with recent data released by the U.S. National Highway Traffic Safety Administration, which highlights how speeding remains a significant threat to motorists. In 2020, the U.S. saw 38,824 traffic related fatalities, of which 11,258 involved speeding accidents, accounting for 29% of all fatal crashes that year.

Data Shows More Risks, Limited Benefits to Raising Speed Limits

In this latest study, AAA Foundation researchers examined 12 U.S. roadway segments between 2014 and 2018. Of the selected sites, three were interstate highways, four were principal arterials (high volume urban roads), three were minor arterials (rural roads) and two were collector roads (low capacity city streets). Six of the selected sites raised their posted speed limits by five miles per hour (mph) during the study period, while six lowered their posted speed limits by 5 to 10 mph.

For all 12 roadways analyzed, researchers compared passenger vehicle crash rates in three categories before and during the study period, including car accident fatalities, car accident injuries, and property damage only car accidents.

According to the findings, those roadways which lowered their speed limits by 5 mph saw less auto accidents injuries, fatalities and property damage.

AAA researchers concluded that lowering speed limits was associated with fewer auto accidents, with minimal effects on traffic and travel time. However, they noted that their findings come as some states move to increase speed limits.

Researchers Find Benefits of Raising Speed Limits are Overrated

As a result of the findings, researchers urged traffic planners to prioritize safety over commute times and traffic volume when setting posted speed limits.

“The movement in statehouses to raise speed limits is happening across the country in at least eight states this year,” Jennifer Ryan, director of state relations for AAA, said in a press release. “But the benefits are overrated, and the risks are understated. Increasing speed limits does not always yield the positive results envisioned by traffic planners.”

The new study aligns with other recently released data suggesting that lowered speed limits significantly reduces car accidents, while only minimally increasing travel times.

A 2020 study determined that speed reduction programs can potentially reduce car accident deaths by more than 20% and lengthen average commute time by only four minutes. Another study released in April this year indicated lower residential and side street speed limits can reduce crash injuries by 17% to 20%.