Raising speed limits leads to more frequent car crashes, while lowering them leads to fewer crashes, a new analysis by AAA concludes. It’s the kind of conclusion that seems obvious on the surface but still needs to be highlighted given how many states seem convinced that raising speed limits can save drivers time, when all it really does is endanger the lives of pedestrians and cyclists.

The report is the latest in a growing body of evidence that finds that changing speed limits can have a big impact on road safety in the US. AAA analyzed a dozen roadways of varying types in the US in which half raised their speed limits while the other half lowered the limit. The group then did a before-and-after assessment to see what kind of impact the altered speed limits had on traffic safety as well as commute times.

Two of the three highways that increased speed limits experienced increased numbers of crashes, injuries, or deaths. Meanwhile, commute times remained “comparable” to where they were before the limits were raised — dashing the expectation that increasing speeds would lead to faster trips for drivers. A number of other road types that raised speed limits did not see a corresponding increase in crashes, injuries, or deaths, leading AAA to conclude that more research is needed.

Lowering speed limits also had a marginal impact on commute times, which could help dash arguments that altering limits come at the expense of travel time and driver convenience.

Speeding is a critical factor in traffic crashes in the US. Speeding-related fatalities recently reached a 14-year high, making up almost one-third of all traffic deaths, according to the National Highway Traffic Safety Administration. This is amid an ongoing “crisis” in road deaths in the US, with traffic fatalities peaking in 2021.

AAA recommends that states apply a “holistic approach” to the question of raising or lowering speed limits, including the type of road, surrounding land use, and historical crash data.

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