Distributed traffic information systems

: theory, simulation and prototype development

Abstract

Distributed traffic information systems (DTIS) are traffic information systems based on inter-vehicle communication. DTIS constitute a developing system that promises greater safety, comfort and convenience in transportation systems. Compared with centralized traffic information systems (CTIS), DTIS require less investment, have stronger resilience to disruptions and disasters and are more suitable for some vital traffic safety applications such as highway collision avoidance and advanced driver assistance systems. A number of projects (e.g., PATH; CarTalk; FleetNet) have explored enabling technologies and applications of DTIS. To guide the future deployment of DTIS, researchers have tried to construct theoretical models and use simulations to investigate DTIS performances under different traffic situations. This thesis conducts its research on DTIS from three perspectives-(1) theoretical model construction, (2) simulation software development, and (3) prototype application design. Firstly, it develops theoretical models to evaluate DTIS performance under different traffic situations. As a decentralized system, DTIS highly relies on inter-vehicle communication (IVC) as its information exchange infrastructure. Due to the limited communication coverage range, IVC depends on wireless-communication relay within traffic streams to transmit information. However, dynamic topology of IVC equipped vehicles (simply referred as "equipped vehicles" later) makes IVC not as reliable as centralized wireless communication. Since whether information can be timely transmitted through IVC to targeted vehicles is essential to the usability of DTIS, to analyze how fast information can be transmitted through IVC becomes an important research question. In this thesis, based on traffic-flow theory, probabilistic models are developed to predict mean value of IVC-message transmission speed, which can be used as indexes of IVC efficiencies. This model could provide analytical results for estimating DTIS performance. It reveals various traffic parameters’ (e.g., traffic density, traffic flow direction, traffic speed, and etc.) effects on DTIS efficiency. These would help DTIS design (e.g., help to decide how many equipped vehicles should be deployed for a certain DTIS service in a city) in the future. Secondly, a software package is developed for simulation of IVC in DTIS. Simulation is an important technique for research of DTIS. Compared with theoretical models, simulation could embrace more complicated traffic settings (e.g., traffic lights, traffic incidents and etc.) and can better help identify these traffic settings’ effects on DTIS. Furthermore, simulation provides an effective way for validating results of theoretical models. Based on a commercial microscopic traffic simulation tool -PARAMICS, a software package for simulations of IVC in DTIS is developed with C++. This software package provides a useful means for understanding how IVC message would spread in complex traffic scenarios. Moreover, theoretical results in this thesis are also verified with the software package’s simulation results. Thirdly, a prototype design of a typical application of DTIS - autonomous traffic-condition collecting & sharing - is conducted in this paper. The prototype design is divided into two parts in this paper. In part 1, the required equipped vehicle population size, which would guarantee the system’s normal functioning, is estimated with proposed theoretical models. In part 2, a prototype device for this application, including hardware part and software part, is developed. IEEE 802.11 a protocol is used as the IVC protocol for test because IEEE 802.11 p is based on IEEE 802.11 a. Experiments are done with prototype devices to show that the proposed application could provide new services to traffic users in real life. In conclusion, this thesis focuses its research on DTIS. Theoretical models and simulation tools are developed to investigate the performance of DTIS under different traffic scenarios. Furthermore, a prototype design for a typical DTIS application is finished in this thesis. The thesis’s contribution could be regarded as threefold: (1) It proposes an effective theoretical model for evaluating DTIS performance; (2) It develops an efficient software package for delicate DTIS simulation; (3) A prototype design is conducted to explore potential DTIS application which could be deployed in the future.

Date of Award	3 Oct 2012
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Shaoyi Stephen LIAO (Supervisor)