Bike in Philly

Img: Pew Charitable Trusts

Let’s say you’re a parent, and you have five kids. Then, let’s say four of those five kids tells you their favorite food is Oreo cookies. The fifth kid says they like grilled chicken, kale, carrots, and fruit.

Would you put all your kids on a strict diet of nothing but Oreos? Probably not.

And would you set all nutritional guidelines according to the kids who are super into Oreos?* Ha!

But that’s how speed limits were once determined, and how some people think they still should be—even in cities.

A search through the Bicycle Coalition of Greater Philadelphia’s blog comments finds more than 30 comments critical of the Bicycle Coalition’s activism for safer speeds throughout Philadelphia, citing something called the 85th Percentile. This may come as a shock (or not!), but the 85th Percentile approach is outdated and should be ignored.

The 85th Percentile idea, based on the 1964 “Solomon Curve” says speed limits should be set at what 85 percent of drivers think is healthy. It was created back when the highway system was still young, cars didn’t approach speeds as quickly as they do today, and we didn’t have the sort of statistics and research on traffic dangers we do today.

This percentile approach has helped create America’s culture of shrugging in the face of death. More than 40,000 people died in motor vehicle crashes in 2016 throughout the United States, costing the country and its people $432 billion. And 4.6 million people were injured on America’s streets. 2016 saw the most traffic deaths in the United States since 2007.

Speed is the leading cause of traffic deaths, and speeding makes it more likely the person involved in the crash will get injured once the crash occurs.

That’s why groups like the Bicycle Coalition – dedicated to making streets safe for all road users – have worked so hard for commonsense legislation like red light and speed cameras in Philadelphia.

I have long trashed the 85th Percentile speed approach as outdated and never meant for cities. That hasn’t stopped some — who feel motor vehicle users should be able to drive as fast as they want — from lashing out at the Bicycle Coalition’s rational attempts to curb speed and make streets safer for everyone.

And the Bicycle Coalition of Greater Philadelphia is not alone. In a huge step toward greater road safety for all, the National Transportation Safety Board released a new study identifying speed-related deaths as an “urgent and under-addressed national problem” in July, calling for an end to the 85th Percentile standards.

Among their specific recommendations: “Revise traditional speed-setting standards to balance 85 percentile approaches with safe systems approach that better incorporates crash history, safety of pedestrians, bicyclists.” Makes sense, considering speed-related deaths are three-times as likely on local roads.

The 85th Percentile rule aims to “accommodate speeding drivers, rather than reduce crashes,” as noted by Streetsblog.

“In general, there is not strong evidence that the 85th percentile speed within a given traffic flow equates to the speed with the lowest crash involvement rate,” the NTSB says. “Alternative approaches and expert systems for setting speed limits are available, which incorporate factors such as crash history and the presence of vulnerable road users such as pedestrians.”

*I cannot take credit for that analogy. I first read it on Rebecca Sanders’ Twitter feed. Thanks Rebecca!

UPDATE: Several organizations have put out press releases about the NTSB’s landmark study. I’ve added some links below. It’s important that cities and municipalities be able to reduce speed now.

NACTO: Federal Study Concludes U.S. Must Change Policies to Curb Epidemic of Deaths Caused by Excessive Motorist Speed

“U.S. streets have long been designed to promote speed at all costs, with deadly consequences,” said Linda Bailey, Executive Director of NACTO. “NTSB’s report is an urgent wake-up call for all walks of government to treat excessive speed as the deadly epidemic that it is. With safe street designs, automated enforcement practices, and policies that prioritize safety over speed, our streets can be modern, inviting places that make cities great places to be.”


“The National Complete Streets Coalition thanks NTSB for taking aim at the critical issue of speeding-related crashes that injure and kill far too many Americans each year — including many on foot or bike. We hope this report will continue to bring attention to the important yet often overlooked role of speeding in traffic injuries and fatalities for everyone who uses our streets…The Coalition is committed to continuing dialogue around speeding-related injuries and fatalities. Thank you to the NTSB team for spotlighting the issue of speeding and traffic safety.”

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