Exploration of 85th percentile operating speed model on horizontal and vertical alignments: A case study for two lane rural highways

The increase number of accidents on two lane rural highways have been linked or related with the problem of inconsistencies on the operating speed and geometric design of highways. Facts showed that traffic collisions have become a major source of social and econometric losses in recent years in Malaysia. The country facing a serious road accident problem and every year for the last five years which more than 5000 people was killed on road. Despite of that, more intention to road safety has to be made so that the traffic collisions due to sub-standard and inconsistency of highway design can be reduced and eliminated. For highway and street design consistency, the quantitative method that has been used mainly by United States is the design speed concept. Whereas, research and experience from other countries such as Germany, Australia and Switzerland indicates that operating speed concept in the design consistency analysis of two lane rural highways is more effective in detecting inconsistencies. This research paper presents an empirical research and presents the new equation to estimate the 85^th percentile operating speed model for the horizontal and vertical curve tangent that reflective on Malaysian rural highways conditions. A speed measurement was taken at twelve sites and regression equations were developed to predict the V85 of vehicles on horizontal and vertical of alignments on two lane rural highways. The developed V85 model presented intends to detect geometric design inconsistencies in most of the horizontal and vertical alignment. And lastly, this research is an attempt to harmonize the designer adoption in selecting and designing highway and the road users' expectation while on the wheels towards an ergonomic approach.