Effects of preceding geometric conditions on operating speed consistency of multilane highways

This paper presents vehicle operating speed models for multilane highways based on preceding geometric conditions. These speed models are required to examine the geometric design consistency of a given road section but have been unavailable on multilane highways because geometric standards are at such high levels that vehicle speed changes are insensitive to geometric conditions. This research deals with this problem by using a nationwide highway database that recently became available, and then investigating drivers' speed changing behaviours on a wider influencing area covering the main and preceding sections of a curve. The approach in the research involves gathering geometric condition and vehicle speed data for many representative multilane highways in South Korea, application of the multiple regression analysis, and developing the relationships between vehicle speeds and geometric conditions. The results show a significant improvement in the predictive power, and this improvement is found to result from having preceding road sections in the model.