First do no harm: Prioritize roadway user safety before raising speed limits

Drivers desiring faster commutes might view a higher speed limit as a boon, but is it always the safest choice? And what about the safety needs of pedestrians, cyclists, and others? A new study by the American Automobile Association (AAA) Foundation for Traffic Safety found that raising posted speed limits may do little to save time and increase traffic flow but could lead to more crashes, injuries, and deaths.

The AAA Foundation’s research results varied across all 12 roadway sites examined. All had new posted speed limits— six raised and six lowered— and included various road types. Raising posted speed limits was associated with increased crashes on two interstate highways. At the same time, the study also found that lowering posted speed limits led to fewer crashes. But the likelihood of speed limit violations increased after lowering posted speed limits, suggesting the need for better public awareness education tied to these changes. AAA urges transportation officials to apply a holistic approach when setting or changing posted speed limits and prioritize safety over speed and capacity.

“Our study analyzed before-and-after data on a dozen roadways that raised or lowered posted speed limits and found no one-size-fits-all answer regarding the impact of these changes,” said Dr. David Yang, president and executive director of the AAA Foundation. “However, it is critical to consider the safety implications when local transportation authorities contemplate making changes with posted speed limits.”

Speeding is a critical factor in vehicle crashes across the nation. According to the National Highway Traffic Safety Administration (NHTSA), there were more than 42,000 traffic deaths in 2021 and again in 2022, the highest levels in 16 years. NHTSA reports that speeding was a factor in nearly 29% of the fatalities in 2021 and 27% in 2022.

The Foundation study found:

• Raising posted speed limits was associated with increased crash frequencies and rates for two of the three interstate highways examined.
• Lowering posted speed limits was associated with decreased crash frequencies and rates for one of the two principal arterials examined.
• Changes in travel times were small in response to both raised and lowered speed limits.

AAA recommends that changes in posted speed limits should consider a range of factors, including the type of road, surrounding land use, and historical crash data. AAA supports automated speed enforcement, but programs must be carefully implemented to maintain community support, prioritize equity and consistently drive improved safety.

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

This study is the third phase of the AAA Foundation research examining the effect of posted speed limit changes on safety. In the Foundation’s first study, traffic engineers were asked how posted speed limits are set and what factors they consider in changing them. In the second phase, crash testing revealed that small speed increases have severe and potentially deadly effects on crash outcomes.