OPERATING SPEED AND RELATION DESIGN BACKGROUNDS:IMPORTANT ISSUES TO BE REGARDED IN MODERN HIGHWAY ALINEMENT DESIGN

摘要

On the basis of three individual, large accident databases, design classes were developed toclassify, from a traffic safety point of view, roadway sections as good, fair or poor designs.In addition operating speed backgrounds were developed for a number of countries includingAustralia, Canada, France, Germany, Greece, Lebanon, and the United States.For the established design classes, it was found that the operating speed backgrounds in thedifferent countries coincided to a large extent. Consequently, these design classes and theircorresponding speed ranges were then taken as the basis for developing an importantcriterion for evaluating sound transitions between individual design elements (curve - curve,tangent - curve) or to detect poor ones.Based on the good, fair and poor design ranges of the developed Safety Criterion, relationdesign backgrounds could be established. By applying relation design , good curvilinearalinements, which are especially favorable in hilly topography, could be achieved. This inturn may improve traffic safety and provide an esthetically pleasing three-dimensionalhighway alinement.However, with respect to flat or mountainous topography, or in case of redesigns,curvilinear aspects do not often lead to optimum solutions. For this reason, the relationdesign considerations are extended in this paper in order to achieve additionally a wellbalanced design between independent tangents and curves.Furthermore, recommendations are given for adequate radii of curve with or withouttransition curves following tangents, for maximum and minimum or desirable tangentlengths, and for tangents that should be regarded as independent or non-independentelements in the design process.Note, that operating speed backgrounds and relation design backgrounds are essential partsof modern highway geometric design tasks, in order to improve traffic safety and to achievesound economic and esthetic solutions.