American Speed Limits Are Based on 1950s Science
Speed limits might make you feel safe, or incredibly frustrated, or both. But either way there's a bigger issue at hand: they're based on outdated data and science from the mid-20th century.
In the US, our speed limits are derived from old studies, like this one from 1964 by traffic systems researcher David Solomon that looked only at rural roads in the 1950s. In line with conventional thinking, Solomon's study fuels the premise that speed limits should be based on the speed at which 85 percent of the drivers on a road are maintaining. That means, if most cars on the highway are going 60 mph, that's what determines the speed limit.
But with around 40,000 people dying in car accidents on American roads every year, something isn't working, John Lower, a transportation engineer in California, told me. That includes the 85 percent formula, which traffic advocates have called for to be repealed. They're calling instead for a data-driven system that reflects the actual traffic using sensor technology. In many cases, this will force us to drive slower.
Lower has spent decades as a city transportation manager, and now works at Iteris, an analytics company. He believes it's time to reinvent the way we implement speed limits. "The way it works now, there are higher-than-expected crash rates along the system," he said.
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