RECOMMENDATIONS RELEVANT TO INTERNATIONAL DESIGN STANDARDS FOR IMPROVING EXISTING (OLD) ALINEMENTS BASED ON SPEED AND SAFETY RELATED RESEARCH

摘要

The design speed- and operating speed concepts as well as sound driving dynamicrnassumptions for tangential and side friction factors are important principles for modernrnhighway geometric design.rnHowever, seventy to eighty percent of the existing road networks in the countries studied sornfar consist of two-lane rural roads with old alinement designs, which frequently revealrnsafety-related deficiencies.rnTo alleviate this problem, three safety-related criteria based on accident research wererndeveloped to evaluate, by quantitative measures, critical situations on existing roadwayrnsections with respect to design-, operating speed-, and driving dynamic consistency.rnFurthermore, these criteria allow to classify new and old alinements according to good, fairrnand poor design practices.rnWhereas, the term operating speed "V85" is nowadays well defined, the term "design speed"rndepends for new designs mainly on road network functions. It should be noted, however,rnthat for the overwhelming majority of existing roadways the design speed is not known orrnwas roughly assessed in the past. Therefore, a new procedure, which takes into account thernoverall characteristics of the roadway, was developed in order to assign sound design speedsrnto old alinements, especially in the case of redesigns. Based on these new design speeds,rnredesigns or RRR-projects can be made by changing the alinement to the extent necessary tornremedy any detected individual or a combined safety problem, while regarding at the samerntime important economic and environmental issues.rnA case study is provided to show how the procedure works in order to evaluate goodrndesigns, examine fair designs, detect poor designs and to establish sound redesigns.rnIn order to compare the actual accident situation with the three safety criteria, thirty casernstudies were analyzed. The results confirm in a convincing manner that the establishedrnclassification system for design-, operating speed-, and driving dynamic classes agreed wellrnto the outcome of large accident data bases.rnThis research includes so far horizontal curvature in full and vertical curvature up to 5 (6)rnpercent. That means, the largest part of the rural road network is covered.