State of the art of highway geometric design consistency

Achieving highway geometric design consistency is an important issue in the design and evaluation of rural highways to attain smooth and safe traffic operation. This paper presents a comprehensive literature review of highway geometric design consistency mainly on two-lane rural highways in North America and Europe. Previous research work on highway geometric design consistency is categorized into three main areas: (1) Speed considerations; (2) safety considerations; and (3) performance considerations. Speed considerations address the different effects of geometric parameters on the prediction of operating speed. Based on operating speed, design consistency of highway elements can be evaluated. Safety considerations explain the different relationships between highway safety and highway/traffic elements, vehicle stability, and low-cost improvements. Performance considerations address the different effects on driver workload, driver anticipation, highway aesthetics, and interchange design. Based on this review, a framework fbr highway design consistency is proposed, and recommendations for future research work on design consistency are suggested, including the need to develop operating speed consistency models based on 3D analysis.