Why the Formula Governing America's Speed Limits Might Be Increasing Road Dangers | Carscoops

      An established formula has been subtly determining speed limits across the U.S. for decades, yet critics argue that it increases risks as cities explore safer options.

      The 85 percent rule, which bases speed limits on driver behavior, has faced criticism for being unsafe.

      Some states and cities are beginning to adopt safety- and context-centric strategies.

      The design of streets often impacts driver speed more significantly than the posted speed limit.

      If you've ever experienced a speed limit that seems too low or unexpectedly high for a road, you're not by yourself. For many years, a single formula has been utilized by multiple states to establish appropriate speeds for vehicles.

      After numerous accidents, close calls, and numerous complaints, some states are starting to reconsider this approach. Even the NHTSA has joined in the push for drivers to reduce their speeds. However, amidst all this discussion, one crucial aspect may be overlooked.

      The Speed Formula

      At the core of this issue is the 85 percent rule, which presumes that the safest speed on a road is the one chosen by the majority of drivers. This premise is significant. Engineers analyze traffic flow, determine the speed at or below which 85 percent of vehicles travel, and round that figure to the nearest five miles per hour. This methodology has influenced speed limits for many years, but critics contend that it has become obsolete and hazardous.

      Safety advocates claim that this rule perpetuates a dangerous cycle: as people drive faster, speed limits are increased, leading to more perilous roads for everyone, including pedestrians, cyclists, and drivers.

      Federal Shift in Guidance

      As reported by the Associated Press, the federal government recently emphasized that the 85 percent figure was not intended to be a rule, suggesting that states should consider additional factors like crash statistics, land use, and pedestrian activity.

      Some cities are already making changes. For example, Madison, Wisconsin, is launching its “20 is Plenty” initiative, which reduces the speed limit from 25 mph to 20 in numerous residential neighborhoods. Similarly, Seattle experienced a reduction in serious injuries after lowering neighborhood speed limits to 20 mph.

      Ohio now permits municipalities to take into account the slower 50th percentile speed in busy pedestrian areas. However, this system does not seem to have universal effectiveness; officials in Boulder, Colorado, report that it had minimal impact on speed reduction.

      Why the Old Rule Persists

      This may explain why many states continue to favor the simplicity of the older system. They receive backing from driver advocates who assert that speed limits should reflect how roads are configured for driving. "The number on a sign is not as significant," states Jay Beeber of the National Motorists Association. "Drivers typically adjust to the nature of the roadway." This is a crucial observation.

      The design of the street often dictates driver behavior more powerfully than the indicated speed. Wide lanes, sweeping curves, and long sightlines encourage faster driving, regardless of whether the speed limit is set at 35 or 55 mph. "It would be unfair for a government to construct a road designed for 45 mph traffic, post a 30 mph limit, and then penalize drivers for adhering to the road's design," Beeber stated.

      Conversely, narrow lanes, sharper turns, and visible pedestrian activities tend to naturally slow drivers down. For states aiming for safer road conditions, rethinking street construction may hold greater importance than merely adjusting speed limits.