Redefining the Fast Lane: Are States Driving Towards a Safer Future by Rethinking Speed?

For decades, the invisible hand guiding speed limits across American roads has largely been the "85th percentile rule." It’s a seemingly simple concept: set the speed limit at or below the speed that 85% of traffic flows, based on the long-held belief that the majority of drivers inherently choose a safe and reasonable speed.

This engineering cornerstone has shaped our highways, but a growing chorus of voices — and an increasing number of state legislatures — are now asking: is "reasonable" fast enough, or too fast, for a truly safe and sustainable future?

The traditional argument for the 85th percentile rule is compelling in its simplicity.

Proponents, like transportation consultant Tony D'Aleo and Robert Wunderlich of the Texas A&M Transportation Institute, argue that it promotes better driver compliance and reduces speed differentials between vehicles, which can actually prevent crashes. They contend that drivers will naturally gravitate towards a speed they deem safe for the road conditions, regardless of the posted limit, making adherence to the 85th percentile a pragmatic approach to traffic management.

Furthermore, it supposedly lessens the burden on law enforcement by aligning limits with actual driver behavior.

However, the tide is turning. Critics, including safety advocates like Charles Farmer and Russ Rader from the Insurance Institute for Highway Safety (IIHS), are sounding the alarm. Their primary concern is undeniable: speed kills.

Higher speeds dramatically increase both the likelihood and severity of crashes. What might be considered a minor fender-bender at 30 mph can become a fatal collision at 50 mph. As Farmer bluntly states, "The more speed, the more severity. It’s a very consistent relationship." Beyond the immediate danger, there are broader implications.

Faster traffic burns more fuel, releases more emissions, contributes to noise pollution, and poses a heightened threat to vulnerable road users — pedestrians, cyclists, and those without the protection of a steel frame around them.

This growing concern is now translating into tangible action at the state level.

Maryland, for instance, has been at the forefront of this shift. In 2022, a groundbreaking law passed, mandating that the State Highway Administration consider a far wider array of factors beyond just traffic flow. Now, crash history, road design, the presence of vulnerable users, environmental impact, equity considerations, and community input must all play a role in determining speed limits.

This legislation also empowers local jurisdictions with greater authority, allowing them to better tailor limits to their unique community needs rather than adhering to a one-size-fits-all engineering formula. While a similar bill in Washington state stalled, it signals a clear legislative interest, and Colorado has explored bills to allow lower limits specifically near schools and pedestrian-heavy areas.

Even Utah is venturing into dynamic speed limits, adjusting speeds based on real-time conditions like weather and traffic.

It’s important to note that no state has entirely abandoned the 85th percentile rule outright. Even the Federal Highway Administration (FHWA), while still supporting the rule, now advocates for a "flexible approach" that incorporates local conditions and community feedback.

This indicates a significant paradigm shift: moving away from a purely engineering-centric model to a more holistic, data-driven strategy that integrates safety, environmental stewardship, and community well-being alongside traffic efficiency. The conversation is no longer just about how fast we can go, but how safely, cleanly, and equitably we can get there.

The speed limit signs of tomorrow may reflect not just the flow of traffic, but the collective values of the communities they serve.