US States Adjust Speed Limits to Match Driver Behavior

The 85% Rule and the Debate Over Speed Limits

For years, Rose Hammond has been advocating for a change in the speed limit on Mitchaw Road in northwest Ohio. This two-lane road passes her assisted living community, a church, two schools, and a busy park that serves as a hub for youth sports leagues. She’s grown frustrated with the lack of action from officials, particularly concerning the motorcycles that frequently speed by. "What are you waiting for, somebody to get killed?" she asked, highlighting the urgency of the issue.

In response to growing public pressure, Sylvania Township requested a review of the speed limit on Mitchaw Road in March. The results were unexpected: the current 55 mph limit is actually 5 mph too low. This revelation has sparked a broader conversation about how speed limits are determined across the United States.

The standard approach, known as the 85% rule, dates back to studies conducted in the 1930s and 1940s. According to this rule, the posted speed limit should reflect the speed at which 85% of drivers travel, rounded to the nearest 5 mph increment. This concept assumes that the safest speed is the one most drivers naturally choose, creating a sort of "vote with your feet" mechanism.

However, some states and transportation experts are beginning to question the validity of this approach. The National Association of City Transportation Officials has developed an alternative called "City Limits," which prioritizes safety over convenience. This method considers factors like pedestrian activity, potential for collisions, and the overall context of the road.

The Federal Highway Administration recently updated its guidelines, signaling a shift away from the 85% rule. While it doesn’t outright reject the rule, it encourages communities to consider other factors, such as road usage, pedestrian risk, and crash frequency. This change has prompted some states to reevaluate their speed limit policies.

In Madison, Wisconsin, the city has launched a campaign called "20 is Plenty," lowering speed limits on local streets from 25 mph to 20 mph. Similarly, Seattle saw a reduction in serious injury crashes after implementing a similar pilot program. These examples highlight the potential benefits of moving beyond the 85% rule.

California remains one of the few states that still heavily relies on the 85% rule. However, recent legislative changes have allowed local governments more flexibility to adjust speed limits based on safety needs. Despite these efforts, advocates argue that more progress is needed to prioritize pedestrians and cyclists.

On the other side of the debate, the National Motorists Association argues that following the 85% rule helps reduce speed variations among drivers. They believe that setting unrealistic limits can lead to unfair enforcement. "It doesn't really matter what number you put on a sign," said Jay Beeber, executive director for policy at the association. "The average driver drives according to the nature of the roadway."

Historically, speed limits have been influenced by various factors, including oil price concerns. In the 1970s, Congress set a national maximum speed limit of 55 mph, which was later relaxed. Today, some states allow speeds as high as 80 or even 85 mph on certain highways. A 2019 study by the Insurance Institute for Highway Safety found that increasing speed limits leads to higher fatality rates, especially on interstates.

Despite these findings, many states continue to rely on the 85% rule. In Ohio, where Mitchaw Road is located, the law sets maximum speeds for different types of roads regardless of the 85% rule. However, the state is gradually evolving its approach, incorporating more consideration for road context and allowing cities to lower speed limits when there's a significant presence of pedestrians and bicyclists.

While the future of Mitchaw Road remains uncertain, the ongoing discussion reflects a broader shift in how speed limits are determined. As communities become more aware of the risks associated with high-speed travel, the push for safer, more inclusive road design continues to gain momentum. For now, Rose Hammond remains hopeful that her advocacy will eventually lead to meaningful change.