Analysis of motorcycle microscopic characteristics at roundabouts under mixed traffic condition: A case study of Vietnam

Recently, the demand for comprehension of mixed traffic in developing countries, particularly at roundabouts, which are highly interactive road junctions, has increased. Thus, we analyzed mixed traffic at roundabouts, considering Vietnam as a case study. The two main objectives of this study were to characterize the mixed traffic in Vietnam and to determine the microscopic characteristics of motorcycles at roundabouts. First, efforts were made to clarify the two constitutions of mixed traffic (the performance rule and the presence of small-sized vehicles), and the term "motorcycle-oriented mixed traffic" was defined. Even when satisfying the two fundamental constitutions, this traffic state has unique features, e.g., only one type of non-lane-based vehicle (the motorcycle) and the predominance of motorcycles in the traffic composition (91.7%). Second, four microscopic characteristics of motorcycles were obtained from a large dataset: the motorcycles' continuous changes in speed, the relationship between the turning angle rate and the speed, the critical gap, and the following space. The relationship between the turning angle rate and the speed was first formulated as a power curve. The critical gap of motorcycles was estimated as a small value (1.25 s) in the case study. The following spaces varied with respect to the speed and had an oval shape. The smallest lateral and longitudinal dimensions were 1.5 and 1.74 m, respectively. While all the findings are meaningful, they are restricted to the case study (Ho Chi Minh City, Vietnam).