A WEB APPLICATION OF FLEXIBLE OPEN-STRUCTURE TRAFFIC SIMULATION

摘要

Traffic simulation is a cost-effective tool to evaluate traffic flow models, network models, traffic control and management strategies, and traffic impact models. It involves utilizing complex models such as object data modeling, behavior models, and other algorithms in routing, randomization, variation etc. However, most existing simulation software packages either provide limited flexibility in customized modeling or require extra proficiency in programming to do so. Therefore, significant amount of effort in transportation research needs to be consumed on non-research-related work such as establish simulation environment from scratch or to bypass the constraints and restrictions in commercial simulation software through complicated API development. In this paper, we present a new web simulation application with several research-and-education-oriented characteristics. First, it separates user interface and simulation engine at the two ends of web. Helper functions are provided by the user interface to build an open-structure simulation workflow. Second, besides modularized structure, each functional component in simulation is defined as a plug-in that can be flexibly interchanged with various simulation models. Third, it also incorporates the use of web applications such as online map, which are served as data sources that eases the processes of generating underlying road network. Last but not least, its online nature of easy accessibility creates a new stage of traffic simulation education. The simulation platform is established on a service-oriented architecture, with core traffic simulation as a web service. Three modules, SimModel, SimEngine and SimFramework, power the platform in data modeling, simulation flow, and user interfaces, respectively. SimModel gives the definition of basic object models, and plug-in interface definition. Four kinds of basic models: 1) fixed objects, 2) moving objects, 3) behaviors, and 4) algorithms roots the categories of data modeling in the platform. Basic implementations of essential functionalities are default for the core traffic simulation. A combined-link-lane GIS model represents the underlying road network by holding geometry simple feature in link and vehicles' movement in lane. Such model takes advantage of both link-based algorithms on high-level simulation, and lane-based models in detailed microscopic simulation. SimEngine functions as the plug-in manager to build customized simulation workflows, to execute the simulation, and to present and analyze the results. Lastly, SimFramework connects the user to the simulation engine with various convenient helper functions, and shows the animation, graphics, and backend simulation running mechanisms for education purposes. Technology-wise, the presented simulation platform was built extensively on advanced web technologies. It employs Model-View-Controller (MVC) concept in modular designs, JavaScript Object Notation (JSON) as primary data transfer format, representational state transfer (RESTful) web services for running simulation, and AJAX for user interaction. It also uses OpenStreetMap (OSM) as main background road network. An algorithm on extracting OSM data and generating link-node network is included in the platform and analyzed in this study. An introduction of a web repository for simulation models and networks is investigated at this time. We argue that such a web-based open-source simulation platform that could plug in interchangeable customized simulation models greatly speed up research and application process. As we adding supplementary features, we are presenting this state-of-the-art simulation platform to the public. Its compactness provides great flexibility while requires generous further contributions from transportation community.