## 1 Introduction  
Vehicular sensor networks (VSNs) are emerging as a new solution for inter-vehicle communication or monitoring urban environments, such as intelligent transportation systems [1]. Recently, many protocols for _ad hoc_ networks have been proposed with the advances in wireless network communications, especially those based on the mobile _ad hoc_ network (MANET) architecture derived from the vehicular _ad hoc_ network (VANET). Although some of the existing _ad hoc_ and sensor network communication protocols can still be applied to vehicular networks (both VSNs and VANETs), simulation results [2,3] have showed that they suffer from poor performances, because of the fast movements of vehicles and limited chances for information exchanges. Furthermore, without a robust infrastructure, nodes (or vehicles) in an _ad hoc_ network may be required to self-organize. Therefore, the design principles for guaranteeing basic performance achievement in an _ad hoc_ network is to make an _ad hoc_ network more stable and further provide scalability and robustness for data dissemination in the network [4]. In general, two kinds of topology control are considered: (1) cluster-based topology control [5, 6, 7]; and (2) distributed topology control [8,9] (Figure 1). In cluster-based topology control, maintaining network connectivity is crucial. An implementation of the linked cluster architecture may consider the following tasks: cluster formation, cluster connectivity and cluster reorganization. However, it suffers from network partitions, which are very common in vehicular networks and may lead to poor system performances, due to a highly dynamic network topology and limited and unstable network resources for communication [10]. In distributed topology control, the main node may use network characteristics and a mobility model to find its group members (e.g., distance, driving direction or speed) for communication and information routing. The conceptual design principles for topology control in VANETs can be found in [11]. In this work, we focus on distributed topology control for achieving effective topology management in a vehicle sensor network. In this category, two major ways to govern mobile nodes are the cone-based scheme [8] and the distance scheme [9]. However, these two schemes may not be effective with regards to node management in the scenarios with changeable moving speeds and directions (e.g., turning left/right). Accordingly, we combine the concepts of these two schemes and propose a hybrid scheme, the hybrid distributed topology control scheme (HDTC), using angle and distance information to form  
Figure 1: Cluster-based scheme (**Left**); distributed scheme (**Right**). a communication group for each vehicle, which relies on a distributed self-configuring protocol [12]. On the basis of the corresponding communication group, a routing group member is further selected to forward the information to the sink vehicle. The key features and contributions of the HDTC are as follows: (1) a distributed topology control scheme is proposed to select the communication members that will participate information exchange; (2) the proposed HDTC scheme combines the strength of the cone-based scheme [8] and the distance scheme [9] to achieve an adaptive topology management for VSNs; (3) extensive experiments are carried out to evaluate HDTC with several scenarios. Our experiment results show that the proposed HDTC algorithm can effectively perform network topology management. Compared with the cone-based scheme and the distance scheme, the proposed HDTC has lower communication complexity and provides a more stable communication network structure for information routing. This paper is organized as follows: Section 2 reviews related works about the topology control problem and information dissemination protocols. Section 3 describes the approach of the HDTC scheme for forming the communication group and determining the routing group members.