Raising speed limits on highways could lead to more crashes on nearby roads, according to new research by the AAA Foundation for Traffic Safety. 

This "spillover effect" creates unintended safety hazards for local communities that might not be involved in the decision-making process to raise the posted speed limit on a nearby highway. According to NHTSA, speeding is a significant safety concern, contributing to almost one-third of road fatalities in the past 20 years.

 AAA Foundation researchers investigated whether changes to posted speed limits on interstate highways could cause drivers to adopt risky speeding behaviors on local streets. The study looked at crash data before and after speed limit increases on interstates in Georgia, Michigan, and Oregon. Hot spot analyses were conducted on roads within a 1-mile radius of interstates. Researchers found many instances where speed-related crashes increased on nearby roads following the interstate speed limit change, suggesting that drivers exiting the highway continued their faster tendencies.

"Increasing posted speed limits on freeways may improve traffic flow but could also lead to safety concerns in adjacent communities once speeding drivers proceed to neighboring roadways,” said Dr. David Yang, president and executive director of the AAA Foundation. Local streets around our homes are designed for slower speeds and diverse road users such as pedestrians and cyclists—not for speeding drivers."

AAA recommends a multi-pronged approach to combat speeding behavior:

By taking a proactive approach, transportation officials can create safer road networks for all communities. The AAA Foundation’s research reinforces the importance of the Safe System Approach (SSA). The SSA is a strategic way of leveraging the engineering and behavioral countermeasures proven effective at preventing traffic crashes and the injuries that can result from them. Explore the Foundation’s guide for implementing the SSA in your community HERE.

"This research has uncovered an unintended but potentially lethal consequence of raising highway speed limits," said Jake Nelson, AAA’s director of traffic safety advocacy. "With the U.S. near a record-high traffic death toll, road authorities can use these findings and an effective tool to pinpoint lifesaving solutions to help ensure that we all get home safely each day."

Previous speeding research by the AAA Foundation found that raising posted highway speed limits is associated with increased crash frequencies in some situations. At the same time, changes in travel times were small in response to both raised and lowered speed limits. 

About the AAA Foundation
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.

About AAA
Started in 1902 by automotive enthusiasts who wanted to chart a path for better roads in America and advocate for safe mobility, AAA has transformed into one of North America’s largest membership organizations. Today, AAA provides roadside assistance, travel, discounts, financial and insurance services to enhance the life journey of over 64 million members across North America, including over 57 million in the United States. To learn more about all AAA offers or become a member, visit AAA.com.