Research On Operational Effects Of Right Turns Followed By U-turns

In recent years, traffic problems in big cities have become more and more serious. In order to enhance transportation circulation efficiency, and to decrease traffic accidents and jams, measures are applied to resolve the traffic problems from aspects of perfect road network constructions, and to strengthen traffic management. Since the road network in big cities has become better constructed, scientific traffic planning, design and management seem to be more and more important.The existence of left-turn flow is an important reason to cause conflicts and traffic jams at intersections. Using right plus U-turn at down stream median openings as an alternative to direct left turns can significantly enhance efficiency and safety of the operation of relative traffic flows.Recently, in China, U-turn has been put into practice at appropriate sites in many cities, and it certainly has acquired good effects. However, over all, the road governor find it untoward and non-objectivity to establish effective projects, especially for the orientation of U-turn sites , the accessorial establishment and the design are lack of theoretic guidance. In addition, because of the randomicity and the irreversibility of traffic phenomena, the design and improvement of right turn plus U-turn and the evaluation of its operational effects are lack of practical criterions.Lately, domestic scholars have committed themselves to study on right turn plus U-turn. Nevertheless, their work is localized on partial and microcosmic lays, instead of considering right turn plus U-turn as an alternative of prohibiting direct left turn as a holistic scheme and evaluating the operational effects systemically and comprehensively.Right turn plus U-turn has been implemented in foreign countries for many years, and the research on the safety and efficiency of this project is plentiful.The pivotal aim of foreign research is practicability, and their research on project design and evaluation is comparatively consummate. But, foreign research was used to using data recursive methods to establish evaluation parameter(travel time, delay, etc.) models. A distinct character of recursive method is that it has a high precision for idiographic sites, but it is not in the ascendant on adaptability, asa result the study its conclusions are short of theoretical value.A prominent spirit of access management is flexibility, which means adjusting measures to local conditions. Most foreign research is based on local data, and there are a great deal of economic, social and cultural differences between China and foreign countries, so it is not appropriate to the copy the conclusions of foreign study to China directly.As the reasons as above, the purpose of this paper is to study the operational process and conflicts via theoretical analysis, and to set up theoretical models that can preferably reflect the relationship between travel time and road traffic conditions. These models are in order to incarnate the running mechanism and process of every interrelated traffic flows under right turn plus U-turn projects, so the methodology is applicable for right turn plus U-turn at any traffic flow and road conditions, giving this study a comparatively high theoretical value.The dissertation is consist of 6 chapters as follows:Chapter1 is the abstract part, the background of this study is recited, the conclusion of the prevenient study is reviewed, the aim and the significance of the study are put forward, the methodology and structure of the dissertation is briefly introduced.In Chapter2, the design standards and principles of right turn plus U-turn projects ,gap acceptance theory and delay theory are briefly introduced, and average waiting time to find a acceptable gap on artery is calculated based on gap acceptance theory, delay at signalized intersections of right turn plus U-turn vehicles is also carefully studied based on delay theory.In Chapter3, the safety and efficiency effects of direct left turn from driveway to artery were carefully studied, the travel time model of direct left turn vehicles were established based on gap acceptance theory.In Chapter4, the safety and efficiency effects of right turn plus U-turn at downstream median opening from driveway to artery were carefully studied,and travel time model of right turn plus U-turn vehicles were established based on gap acceptance theory.In Chapter5, the safety and efficiency effects of right turn plus U-turn at downstream signalized intersections from driveway to artery were carefully studied, thus travel time model of right turn plus U-turn vehicles were established based on gap acceptance theory and delay theory at signalized intersections. Inaddition, safety effects of the three methods are compared and the results are put into a table.Chapter6 is the sum-up part, in which the primary work, the final conclusion , the significance and the applied fields of this dissertation are briefly depicted, the subsequent work need to be accomplished is also conceived.Chapter2 to Chapter5 are the primary part of this dissertation.Chapter2 is the basis of Chapter3 to chapter5, which are the pivotal part of the study, in which operational effects of direct left turn, right turn plus U-turn at downstream median openings and right turn plus U-turn at downstream signalized intersections are studied from the point of view of safety and efficiency, being of help for the transportation agencies to manage left turns and crossing movements on multilane highways.