Traffic Characteristics and Behavior of Mixed Traffic Flow for Roundabout
|關鍵字:||圓環;微觀車流;混合車流;機車;車流特性與行為;Roundabout;Microscopic traffic flow;Mixed traffic;Motorcycle;Traffic characteristics and behavior|
The motorcycle ownership rate in Taiwan is high. Motorcycles are small in size, lighter weight and high mobility, and the characteristics are significantly different from those of passenger cars. Motorcyclists are more easily to do overtaking and filtering than cars. Roundabouts are widely used in urban areas. That could increase safety and operational performance, and is sometimes used in urban city to preserve a heritage. Generally, there are two indexes, safety and capacity, to evaluate the roundabout performance. Some traffic characteristics need to be analyzed before the study evaluates the roundabout performance. Previous study point out that the characteristics of mixed traffic and passenger car traffic on the urban arterials are different. This study infer that they are also different on roundabout. However, previous study relative to roundabout only focus on the passenger car traffic, the result may not be appropriate to apply to the high motorcycle ownership rate region. The objective of this study is to propose a process about how to use the microscopic traffic dataset to analyze traffic characteristics and behavior of mixed traffic flow for roundabout. This study adopted an aerial videography approach to collect the video using a drone. Videos are converted into microscopic traffic data in the form of vehicle trajectories, in which the characteristics and parameters of interested can be extracted from the dataset. The mixed traffic characteristics and behavior, such as lane usages, speed, acceleration, deceleration, lateral position, lane changing and lag acceptance are analyzed. The data extracted from the trajectory extraction software is in Cartesian coordinate system. In order to determine which lane the vehicle used at each data point, the computation is more convenient if the positions and trajectories of vehicles are in Polar coordinate system. The vehicles move along a curve in a roundabout, and it is not appropriate to use the straight line distance between two consecutive data points to represent the distance travelled. A quadratic function is used to fit in the coordinates of the data points before and after the time instances, and the distance travelled in a time interval is estimated by integrating the function over the time interval. The preliminary results show that there are significant differences in terms of lane choices, speed distribution and frequency of lane changing times between motorcycles and passenger cars at different locations of a roundabout. This study also found that the car drivers didn’t abide by the lane discipline on roundabout because the drivers change the lane frequently. The number of lane changing times would affect by the travel distance and how many entrance or exit the vehicle passed, and are different from cars and motorcycles. The result of critical lag show that there are differences under different combination of objective vehicle mode and conflict vehicle mode. Future research could follow this process to study the characteristics and behavior of mixed traffic for other roundabout. The next step is to investigate the interactions between vehicles, such as overtaking and filtering behavior of motorcycles (Wong and Lee, 2015). The derived characteristics and interactions can be further used for the development, calibration and validation of behavioral models of vehicles in a roundabout. The results can also be applied to the evaluation of roundabout performances for capacity and safety.
|Appears in Collections:||Thesis|