SAFETY-BASED CAPACITY ANALYSIS FOR CHINESE HIGHWAYS: A Preliminary Study

Abstract

Many years of research have led to the development of theories and methodologies in roadway capacity analysis in the developed countries. However, those resources coexist with roadway design and traffic control practices in the local country, and cannot be simply transferred to China for applications. For example, the Highway Capacity Manual in the United State describes roadway capacity under ideal conditions and estimates practical capacities under prevailing conditions in the field. This capacity and the conditions for change are expected to be different on Chinese roadways as the local roadway design (lane width, curves and grades), vehicle size, and traffic mix are different. This research looks into an approach to the capacity issue different from the Highway Capacity Manual. According to the car-following principle, this paper first describes the safety criteria that affect traffic operations. Several speed schemes are subsequently discussed as they are affected by the maximum speed achievable under the local conditions. The study has shown that the effect of geometric and traffic conditions can be effectually reflected in the maximum speed adopted by the drivers. For most Chinese highways without a posted speed limit, the choice of speed by the drivers from the safety prospective is believed to have incorporated considerations of the practical driving conditions. Based on this, a condition for capacity calculation is obtained by comparing the desired vs. safety-based distance headways. The formulations of the model are mathematically sound and physically meaningful, and preliminary testing of the model is encouraging. Future research includes field data acquisition for calibration and adjustment, and model testing on Chinese highways.