Analysis of information sources in references of the Wikipedia article "設計速率" in Chinese language version.
Because of differences in design and operation criteria, there are locations where the posted speed limit based on an 85th percentile speed exceeds the roadway's design speed. This situation is because criteria used in highway design incorporate a significant factor of safety. Consequently, it is not surprising that motorists feel comfortable traveling at speeds greater than the roadway's design speed during good weather conditions. ... Although it is obvious that the "maximum" safe speed can be exceeded without difficulty on vertical and horizontal curves when good weather conditions are present, it is difficult to convince the general public that a roadway's design speed can be exceeded with safety.
A significant concern with the 1954 design speed concept was the language of the definition and its relationship with operational speed measures. The term "maximum safe speed" is used in the definition, and it was recognized that operating speeds and even posted speed limits can be higher than design speeds without necessarily compromising safety. In 1997, Fambro et al. (15) recommended a revised definition of design speed for the Green Book while maintaining the five provisions noted above. The definition recommended was, "The design speed is a selected speed used to determine the various geometric design features of the roadway." The term "safe" was removed in order to avoid the perception that speeds greater than the design speed were "unsafe". The AASHTO Task Force on Geometric Design voted in November 1998 to adopt this definition and it was included in the 2001 Green Book (17).
Arbitrarily setting lower speed limits at point locations due to a lower inferred design speed is neither effective nor good engineering practice.
Because of differences in design and operation criteria, there are locations where the posted speed limit based on an 85th percentile speed exceeds the roadway's design speed. This situation is because criteria used in highway design incorporate a significant factor of safety. Consequently, it is not surprising that motorists feel comfortable traveling at speeds greater than the roadway's design speed during good weather conditions. ... Although it is obvious that the "maximum" safe speed can be exceeded without difficulty on vertical and horizontal curves when good weather conditions are present, it is difficult to convince the general public that a roadway's design speed can be exceeded with safety.
A significant concern with the 1954 design speed concept was the language of the definition and its relationship with operational speed measures. The term "maximum safe speed" is used in the definition, and it was recognized that operating speeds and even posted speed limits can be higher than design speeds without necessarily compromising safety. In 1997, Fambro et al. (15) recommended a revised definition of design speed for the Green Book while maintaining the five provisions noted above. The definition recommended was, "The design speed is a selected speed used to determine the various geometric design features of the roadway." The term "safe" was removed in order to avoid the perception that speeds greater than the design speed were "unsafe". The AASHTO Task Force on Geometric Design voted in November 1998 to adopt this definition and it was included in the 2001 Green Book (17).
Arbitrarily setting lower speed limits at point locations due to a lower inferred design speed is neither effective nor good engineering practice.
