85th percentile speed
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The 85th percentile speed or 85th percentile rule is a traffic engineering standard used to set the speed limit for automobiles on a public roadway.[1] It refers to a speed where 85% of vehicles travel at or below.[2][3][4][5]
Critics of the guideline say that it is inappropriate to let drivers set the speed limit for a road via their own recorded speed.[2][4] Once a speed limit has been set using the 85% rule, motorists tend to drive faster than that new speed limit.[2][4] A speed limit set using this methodology also does not take into account the safety of pedestrians in the area or bicyclists using the road.[2][4][6]
Public safety advocates have advocated for the Federal Highway Administration to change their guidance on the usage of the 85th percentile rule in updates to Manual on Uniform Traffic Control Devices.[6]
See also[edit]
- Design speed
- Vision Zero, policy to minimize pedestrian fatalities
References[edit]
- ^ Taylor, Brian D.; Hong Hwang, Yu (June 30, 2020). "Eighty-Five Percent Solution: Historical Look at Crowdsourcing Speed Limits and the Question of Safety". Transportation Research Record. 2674 (9): 346–357. doi:10.1177/0361198120928995. Retrieved May 25, 2024.
- ^ a b c d Tchir, Jason (May 30, 2021). "Shouldn't speed limits be designed for the '85th percentile' of drivers?". The Globe and Mail. Archived from the original on June 2, 2021. Retrieved May 15, 2024.
The 85th percentile is an old tool for setting speeds on new roads, experts say – but it doesn't mean all limits should be decided by the fast crowd. 'It's got a history that goes back 50-plus years,' said Jeff Lindley, chief technical officer for the Institute of Transportation Engineers (ITE). 'Over the years, I would say there has been an overreliance on [the 85th percentile] as a way to set and adjust speed limits in a way that wasn't intended.'
- ^ McKinley, Jesse (March 23, 2023). "Is 70 M.P.H. the New 65? Legislators Say N.Y. Roads Are Just Too Slow". The New York Times. Retrieved September 15, 2023.
States set speed limits using a variety of methods and measurements, including the so-called 85 percentile rule, which refers to the speed 'at or below which 85 percent of the drivers travel on a road segment', according to the Federal Highway Administration.
- ^ a b c d Minor, Nathaniel (September 15, 2023). "A lower speed limit could be coming to a Colorado road near you". Colorado Public Radio. Retrieved September 15, 2023.
Traditionally, U.S. traffic engineers use the '85th percentile' method that sets limits at the speed at or below which 85 percent of drivers travel in normal conditions. This federally approved approach has been used by state and local transportation agencies since at least the '60s, but street safety advocates and city transportation officials deride the method because it usually leads to higher speed limits and faster speeds, which is associated with more serious crashes.
- ^ "Setting Speed Limits". Institute of Transportation Engineers. Retrieved January 18, 2024.
- ^ a b Sánchez, Vanessa G. (May 25, 2024). Written at Los Angeles. "'So Much Death': Lawmakers Weigh Stricter Speed Limits, Safer Roads for Pedestrians". U.S. News & World Report. Washington, D.C. KFF Health News. Retrieved May 25, 2024.
Road safety advocates argue the federal government missed an opportunity to eliminate outdated standards for setting speed limits when it revised traffic guidelines last year. The agency could have eliminated guidance recommending setting speed limits at or below how fast 85% of drivers travel on uncongested roads. Critics contend that what's known as the 85th percentile rule encourages traffic engineers to set speed limits at levels unsafe for pedestrians.
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