On May 1st, traffic engineers in the state of Oregon will no longer rely on an outdated and dangerous method for setting speed limits. Thanks to new rules adopted by the Oregon Transportation Commission last month, the process for for designating speeds has changed dramatically and now goes way beyond the traditional 85 percentile method.
The 85th percentile rule has dominated U.S. traffic engineering since it was championed in the 1960s. It says limits should set at the speed which 85% of drivers are currently driving at or under. What could possibly go wrong? Since it’s a universal phenomenon that people drive faster than what’s safe, this methodology is very biased toward higher speeds and it’s a big factor in America’s rising traffic death toll.