Safer Roadways: A Complete Streets Guide 36 adjacent land, thereby increasing its value, and therefore is appropriate for the surrounding context. Features associated with high‐speed designs, such as large curb radii, straight and wide travel lanes, ample effective clear zones (no on‐street parking or street trees), guardrails, etc., degrade the walking/biking experience. A slower design speed allows the use of features that enhance the walking/biking environment; they include small curb radii, narrower sections, trees, on‐street parking, curb extensions, and street furniture, which in turn slows traffic. Context appropriate speed is discussed in Chapter Three, Street Typologies. Design streets using target speed, the speed you intend for drivers to go, rather than operating speed. Use design criteria that are at or below the target speed of a given street. The use of higher speeds should be reserved for limited access freeways and highways and is inappropriate on other streets, including arterials 11 . Design speed can be brought into alignment with the target speed by implementing measures to reduce and stabilize operating speeds as appropriate. Narrower lane widths, roadside landscaping, speed humps and raised intersections, and curb extensions are some design features that reduce traffic speeds and improve the quality of the bicycle and pedestrian realm. How speed limits are set has received a lot of attention by various safety organizations such as the National Highway Traffic Safety Administration and US Department of Transportation (USDOT) and by professional organizations such as NACTO and ITE. The attention is focused on the current system that rewards drivers who speed, forcing higher 85 th Speed Posting Process
percentile speeds, that ultimately result in higher posted speeds. State and local transportation agencies set speed limits by completing engineering speed studies and following the guidance presented in the Manual of Uniform Traffic Control Devices (MUTCD). There are three base methods to set speed limits including the 85 th percentile
method, the USLIMITS2 method, and the Safe Systems Approach. USLIMITS2 recommends setting speeds closer to the 50 th percentile speed. The 85 th percentile speed setting method is based on the premise that the majority of drivers choose reasonable speeds for given road conditions and should be accommodated. However, with time, this premise has been shown to be fallible. If applied, this system leads to higher operating speed and an undesirable cycle of speed escalation resulting in higher exposure for users that has resulted in higher rates of crashes and fatalities. The MUTCD’s recent Notification of Planned Amendments for the upcoming 11 th Edition will be recommending posted speed limits to be within five MPH of the 85 th percentile speed only on Freeways, Expressways and Rural highways. New support documentation directs
11 National Association of City Transportation Officials (NACTO), Urban Street Design Guide
Made with FlippingBook Learn more on our blog