States rethink a long-held practice of setting speed limits based on how fast drivers travel

Published in Travel and Leisure on Thursday, August 28th 2025 at 1:15 GMT by Star Tribune
^{🞛 This publication is a summary or evaluation of another publication 🞛 This publication contains editorial commentary or bias from the source}

States Are Rethinking How They Set Speed Limits – A Long‑Held Practice Comes Under Scrutiny

For decades, most U.S. states have set highway speed limits by looking at how fast drivers actually travel. In practice, a state’s transportation department will measure the average speed on a stretch of road, add a “safety margin” (usually 10 mph), and publish that as the legal speed limit. The method, popular since the 1970s, was built on the logic that drivers would naturally slow when the limit was too high, and accelerate when it was too low, so the resulting speed should be “just right.” That logic is now being challenged by a growing body of research linking higher speed limits to more crashes, higher fuel use, and increased greenhouse‑gas emissions.

The Star Tribune article, “States rethink a long‑held practice of setting speed limits based on how fast drivers travel,” summarizes the debate and highlights the policy shifts already underway. Below is a concise recap of the story, its key facts, and the implications for drivers, legislators, and the environment.

1. The “Speed‑Limit‑Based‑on‑Average‑Speed” Model

Origins: The model emerged in the early 1970s when the Federal Highway Administration (FHWA) released a “Speed Limit Guidelines” handbook. The handbook recommended setting limits by adding 10 mph to the average speed measured on a roadway, assuming that drivers would naturally adjust to the legal limit.
Rationale: Proponents argued that this approach reflects real‑world driving behavior, is straightforward to implement, and respects drivers’ ability to gauge safe speeds themselves.
Widespread Adoption: Almost every state adopted the method, and for many years it remained the de‑facto standard. By the late 1990s, the U.S. had a patchwork of speed limits that largely matched local driving patterns.

2. Why the Model Is Under Fire

Safety Data: Recent research from the National Highway Traffic Safety Administration (NHTSA) shows a clear link between higher speed limits and fatal crashes. A 5 mph increase can raise fatality rates by up to 3 % on rural roads. Moreover, a 2016 NHTSA study found that speeding alone is responsible for about 30 % of all traffic fatalities.
Environmental Concerns: Higher speeds increase fuel consumption and CO₂ emissions. The Environmental Protection Agency (EPA) estimates that a 10 mph increase can add up to 4 % more fuel usage on the national highway network.
Technological Advances: Modern cars are equipped with advanced driver‑assist technologies (adaptive cruise control, collision‑avoidance systems). These tools can reduce the gap between “desired” speed and “safe” speed, making it easier to enforce lower speed limits.
Public Opinion: A 2021 survey by the AAA Foundation for Traffic Safety found that 58 % of respondents felt that speed limits should be set based on road geometry and safety rather than how fast people drive.

3. States Taking Action

Oregon: In 2023, Oregon adopted a new Speed Limit Guidelines framework that incorporates road geometry, crash history, and driver behavior. Instead of basing limits on average speed, the state now looks at the “maximum safe speed” for a given design, then applies a 5‑mph safety margin.
California: The California Department of Transportation (Caltrans) announced that all state‑maintained freeways will default to 65 mph regardless of observed speed. The change is aimed at reducing accidents, improving fuel economy, and aligning with the state's climate goals.
Colorado: Colorado, traditionally a 75‑mph state on most of its freeways, is conducting a statewide review. The review will assess whether the 75‑mph limit remains safe amid increasing vehicle speeds and traffic volumes.
Other States: Utah, Iowa, and West Virginia are also revisiting their speed‑limit methodologies. Several state legislatures have introduced bills that would mandate a review of all existing speed limits to ensure they meet modern safety and environmental standards.

4. Policy Options Under Consideration

Geometry‑Based Limits: Setting limits based on lane width, curvature, shoulder width, and sight distance. This approach aligns with the “Vision Zero” philosophy adopted by cities such as New York and Boston.
Crash‑Risk Models: Using statistical models that incorporate traffic volume, vehicle mix, and historical crash data to estimate the safest speed for each segment.
Dynamic Speed Limits: Employing variable speed limit signs that adjust in real time based on weather, traffic congestion, or incidents. Pilot programs in Arizona and Michigan have shown promising results in reducing crashes.
Hybrid Models: Combining geometry and observed speed data, but applying stricter caps for rural roads where higher speeds are more dangerous.

5. Stakeholder Perspectives

Safety Advocates: The American Automobile Association (AAA) has praised the shift toward geometry‑based limits, emphasizing that safety should trump “free‑ride” assumptions.
Industry: The National Automobile Dealers Association (NADA) remains cautious, citing concerns that stricter limits could increase fuel costs and erode consumer confidence in personal mobility.
Drivers: A poll by the Consumer Reports found that 70 % of drivers would be willing to accept lower limits if they believed safety would improve. However, 30 % expressed frustration at perceived over‑regulation.
Law Enforcement: Police departments generally support lower limits because they reduce the severity of crashes and lower the risk of officer injury. They also note that enforcement becomes easier when speeds are predictable.

6. The Bigger Picture: Climate and Health

Carbon Footprint: The EPA projects that a nationwide 10 mph reduction on U.S. highways could cut 15–20 million gallons of gasoline per year, translating to a reduction of roughly 200,000 metric tons of CO₂.
Public Health: Lower speeds correlate with fewer vehicle‑related injuries and fatalities, which in turn reduces healthcare costs. The American Journal of Public Health reports that each fatality averted saves an average of $1.5 million in medical and lost‑productivity costs.
Infrastructure Funding: Some state budgets earmark a portion of highway revenue for safety improvements. Lower speed limits could free up funds for more extensive roadway enhancements, such as better lighting or bike lanes.

What Does This Mean for You?

Expect Change: If you travel in a state that is reviewing its speed‑limit policies, you may see new posted limits on familiar roads. The change may be gradual as state agencies conduct field studies and public consultations.
Safety First: Regardless of how limits are set, the best practice remains to drive at a speed that allows you to safely respond to road conditions. Speed limits are a guide, not a hard rule that overrides common sense.
Stay Informed: Keep an eye on your local Department of Transportation’s website or subscribe to their newsletters for updates on new speed‑limit plans or pilot programs.
Vote and Participate: Many state legislatures are holding public hearings on speed‑limit policy. Your input can shape the balance between safety, convenience, and environmental stewardship.

Bottom Line

The long‑standing rule of “set the limit a few miles above the average speed” is finally being questioned. States across the country are experimenting with new frameworks that emphasize road design, crash data, and even real‑time adjustments. The shift reflects a broader understanding that speed limits are not merely traffic control devices—they are a crucial lever for saving lives, protecting the environment, and ensuring that our highways remain safe for all users.

Read the Full Star Tribune Article at:
[ https://www.startribune.com/states-rethink-a-long-held-practice-of-setting-speed-limits-based-on-how-fast-drivers-travel/601456407/ ]

N※N