A study of the relationships between road access, traffic safety and travel speed, and applications to access planning and speed zone design

This thesis investigates the impacts of highway access on traffic safety and traffic operation efficiency, and develops a model for planning access provisions. A comprehensive data base was created for the analyses by taking advantage of an existing photographic log of selected sectional highway information for one Canadian province. The data base includes information on access types, access density, traffic volume, speed limit, geometry, and accident records. A review of the existing traffic situation and an examination of some established relationships of access and accidents indicated a need to update current knowledge of the impact of highway access. Accident models are developed with particular emphasis on access and its combined effects with traffic volume and road geometric factors on highways. Furthermore, a conceptual hazard model is developed which includes traffic conflicts as additional information to extend the knowledge of access as a road hazard. The literature on access and traffic operation relationships is sparse, particularly on two-lane highways, perhaps because of the high cost of comprehensive data collection for this complex problem. Consequently the present investigation is restricted to the use of a surrogate of average travel speed to define access and speed relationship. In addition to the investigation of access impact, a framework for determining the optimal number of access points is formulated to help to set up access planning criteria. The optimization process is the application of the defined relationships between access and traffic safety and operations in highway planning and design. The process minimizes the total social cost as an integer nonlinear programming problem, solved by piecewise approximation. Finally, the relevant issues of access and speed zone design are addressed, in which particular attention is given to deriving speed transition zone length. The derived accident models show that accesses are major contributing factors of accidents on all types of highways. In some situations, the combined effects of access and geometric factors undermine further the safety level. The analysis for two-lane highway indicates that non-linear relationships may exist between accesses and travel speed. The derived optimization framework for planning access provisions provides a quantitative base for functional classification of roads. In traffic control design, a procedure of speed zone design is outlined with consideration of access provisions.Applied Science, Faculty ofCivil Engineering, Department ofGraduat