AARoads Forum

National Boards => General Highway Talk => Traffic Control => Topic started by: ElishaGOtis on February 26, 2025, 09:49:02 AM

Title: 50th Percentile & Rounded-Down 85th Percentile Speed Limits
Post by: ElishaGOtis on February 26, 2025, 09:49:02 AM
Recently, there's been another push against using the traditional 85th percentile method of modifying speed limits, with a few alternatives being the "rounded-down" 85th percentile (I.e. get an 85%ile of 44, round down to speed limit 40), the 50th percentile / median (either closest or rounded-down), and the interval-offset 85th percentile (I.e. 85%ile of 72, subtract 10 or another specified interval, round, speed limit 60).

Despite many speed limits to this day still being significantly lower than any of these values (can YOU drive 55? :spin: ), are there any examples of speed limits being set or modified using these statistics?

This is a slightly different focus than "twenty's plenty" or other safe-systems approaches, as those completely disregard operating speed when setting the limit.
Title: Re: 50th Percentile & Rounded-Down 85th Percentile Speed Limits
Post by: 1995hoo on February 26, 2025, 10:49:28 AM
Quote from: ElishaGOtis on February 26, 2025, 09:49:02 AM....

Despite many speed limits to this day still being significantly lower than any of these values (can YOU drive 55? :spin: ) ....

I remember when I was in law school in the mid-1990s, I found a road on which I was very happy driving 55 mph.

Problem: The road was Hope Valley Road in Durham, North Carolina, and the speed limit was 35.