Impact of highway consistency on capacity utilization of two-lane rural highways

Consistent highway design is expected to provide safe, economical, and smoo th traffic operation. Several studies have been performed to investigate th e effect of highway consistency on traffic safety. However, the relationshi p between design consistency and highway capacity and level of service has not been addressed in current research work and design practices. In additi on, the effect of the three-dimensional (3D) nature of highway alignments w as not considered, and design consistency was studied based solely on two-d imensional (2D) analysis of highway horizontal alignments. This paper prese nts a methodology to determine the effect of highway design consistency on highway capacity utilization based on 3D analysis. This methodology will he lp road designers to estimate highway capacity more accurately. The study w as performed on two-lane rural highways in Ontario, where two types of 3D c ombinations were considered: a horizontal curve combined with a sag vertica l curve (sag combination) and a horizontal curve combined with a crest vert ical curve (crest combination). An additional adjustment factor that reflec ts the effect of highway design consistency on capacity utilization was dev eloped. Different statistical models are introduced to estimate this factor based on geometric or traffic data. In addition, typical values of the con sistency factor were developed based on an overall consistency evaluation c riterion and can be easily used in capacity analysis.