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 Am
erica and Europe. Previous research work on highway geometric design consis
tency is categorized into three main areas: (1) Speed considerations; (2) s
afety considerations; and (3) performance considerations. Speed considerati
ons address the different effects of geometric parameters on the prediction
of operating speed. Based on operating speed, design consistency of highwa
y elements can be evaluated. Safety considerations explain the different re
lationships between highway safety and highway/traffic elements, vehicle st
ability, and low-cost improvements. Performance considerations address the
different effects on driver workload, driver anticipation, highway aestheti
cs, and interchange design. Based on this review, a framework fbr highway d
esign consistency is proposed, and recommendations for future research work
on design consistency are suggested, including the need to develop operati
ng speed consistency models based on 3D analysis.