What is the 85% rule?
The 85% rule is a guideline that suggests a road's speed limit should be set at or near the speed at which 85% of vehicles travel.
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Transportation / Road Safety
Rethinking Speed Limits: Moving Beyond Driver Behavior
For decades, the 85% rule has heavily influenced how speed limits are set in the U.S. This rule suggests that a road's posted speed should align with the speed at which 85% of vehicles travel. However, amid rising concerns about road safety...
Key Insights
- The 85% rule, dating back to the 1930s and 1940s, sets speed limits based on the speed most drivers naturally travel.
- Critics argue this creates a feedback loop where speeding leads to increased speed limits. **Why this matters:** This can compromise the safety of pedestrians, cyclists, and other vulnerable road users.
- The Federal Highway Administration (FHWA) has clarified that the 85% rule isn't a rigid requirement and that communities should consider factors like road usage and pedestrian risk.
- Alternative approaches, such as the "City Limits" system, consider activity level and conflict density to minimize injury risks.
- Cities like Madison, WI, and Seattle, WA, have seen positive results from lowering speed limits on residential streets.
In-Depth Analysis
### Background The 85% rule assumes the safest speed is the one most vehicles travel. However, this approach has been criticized for encouraging higher speeds and neglecting the safety of pedestrians and cyclists.
### The Shift The FHWA's update to the Manual on Uniform Traffic Control Devices signals a move towards a more holistic approach to setting speed limits. This shift encourages communities to consider: - Road usage - Risk to pedestrians - Frequency of crashes
### Alternative Approaches The "City Limits" system, developed by the National Association of City Transportation Officials, offers an alternative to the 85% rule. It sets speed limits based on: - **Activity Level:** The type of area the road is in (e.g., downtown, suburban). - **Conflict Density:** The number of intersections, driveways, and curb cuts per quarter-mile.
### Real-World Impact - New York City's Vision Zero program, which prioritizes pedestrian safety, has led to a 30% drop in traffic injuries and significant Medicaid savings. - Seattle saw a noticeable decline in serious injury crashes and a 7% drop in the 85th percentile speed after implementing a pilot program to lower speed limits.
FAQ
Why are states rethinking the 85% rule?
Because it can lead to increased speed limits and compromise the safety of pedestrians and cyclists.
What is the "City Limits" system?
It's an alternative approach that considers activity level and conflict density to set speed limits.
Takeaways
- The way speed limits are set is evolving to prioritize the safety of all road users.
- The 85% rule is no longer considered the sole standard for determining speed limits.
- Communities are encouraged to consider road usage, pedestrian risk, and crash frequency when setting speed limits.
- Alternative approaches like "City Limits" offer a more holistic way to determine safe speed limits.
Discussion
Do you think this shift away from the 85% rule will make roads safer? Let us know in the comments!
Share this article with others who need to stay ahead of this trend!
Sources
Disclaimer
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