Highway geometric design consistency: Speed models and local or global assessment

The geometric design of a road based on consistency implies that this should not violate driver expectations. although there are different methods for estimating consistency,the most used have been those based on the operating speed of vehicles. this is due to its relationship with accidents. road alignments which cause marked differences in vehicle speeds favour a greater accident rate. in this research,local approaches to evaluate the consistency of the alignments (tangents,curves) versus global approaches to evaluate an entire stretch of road have been analyzed. different models have been used to estimate an operating speed of vehicles. the study has focused from a practical point of view using two applications for the evaluation of consistency of a stretch of road. the results show the influence of the choice of the speed model in the level of consistency. in addition,practical issues about how some variables,such as desired speed,posted speed,and design speed,can influence the results that are presented. � iran university of science and technology 2016.