AAA Research finds minimal benefits, increased risks from raising speed limits

PORTLAND, Ore., (July 13, 2023) Many think that raising speed limits can help drivers get to their destinations more quickly. But new research from the AAA Foundation for Traffic Safety shows that raising speed limits may do little to save time and can lead to more crashes, injuries, and deaths. Higher speeds can also make roads less safe for pedestrians and cyclists.

The AAA Foundation examined 12 roadway sites across the U.S. including five in Oregon (see the list below). 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. Lowering posted speed limits led to fewer crashes in many cases.

“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 major factor in vehicle crashes across the U.S. 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.

In Oregon, there were 599 traffic deaths in 2021, and the preliminary number for 2022 is 600 traffic deaths, according to the Oregon Department of Transportation Crash Statistics & Reports. Driving too fast for road conditions and exceeding the posted speed limits are major factors in Oregon crashes.

“Raising speed limits is often thought of as a way to improve traffic flow and to allow drivers to get to their destinations more quickly. However, our AAA research shows that driving at higher speeds increases risk which can outweigh the potential benefits of saving a few minutes of time,” says Marie Dodds, public affairs director for AAA Oregon/Idaho.

Key Findings from the AAAFTS Study:

  • 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.

Find all the details in the research brief.

AAA recommends that changes in posted speed limits should consider a range of factors, including but not limited to the type of road, surrounding land use, historical crash data, and how changes in speed limits impact the safety of other road users including pedestrians and bicyclists.

Five of the 12 roadways studied are in Oregon:

  • 291 miles of I-84
  • S.E. Division Street in Portland
  • North Lombard Street/U.S. 30 Bypass in Portland
  • NE Marine Drive in Portland
  • S.W. Capitol Highway in Portland

On I-84, the speed limit was raised from 65 to 70 mph. On Division St., the speed limit was lowered from 35 to 30 mph. On North Lombard Street/U.S. 30 Bypass in Portland, the speed limit was lowered from 35 to 30 mph. On N.E. Marine Drive in Portland, the speed limit was lowered from 40 to 35 mph. On S.W. Capitol Highway in Portland, the speed limit was lowered from 35 to 25 mph.

About the AAA Foundation for Traffic Safety

Established in 1947 by AAA, the Foundation for Traffic Safety is a nonprofit, publicly funded 501(c)(3) charitable research and educational organization. The AAA Foundation’s mission is to prevent traffic deaths and injuries by researching their causes and by educating the public about strategies to prevent crashes and reduce injuries when they do occur. This research informs the development of educational materials for drivers, pedestrians, bicyclists, and other road users. Find out more at

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