The dynamic nature of vehicular ad hoc network (VANET) induced by frequent topology changes and node mobility, imposes critical challenges for vehicular communications. Aggravated by the high volume of information dissemination among vehicles over limited bandwidth, the topological dynamics of VANET causes congestion in the communication channel, which is the primary cause of problems such as message drop, delay, and degraded quality of service. To mitigate these problems, congestion detection, and control techniques are needed to be incorporated in a vehicular network. Congestion control approaches can be either open-loop or closed loop based on pre-congestion or post congestion strategies. We present a general architecture of vehicular communication in urban and highway environment as well as a state-of-the-art survey of recent congestion detection and control techniques. We also identify the drawbacks of existing approaches and classify them according to different hierarchical schemes. Through an extensive literature review, we recommend solution approaches and future directions for handling congestion in vehicular communications.

频繁的拓扑变化和节点移动性导致的车辆自组织网络（VANET）的动态性质对车辆通信提出了严峻的挑战。VANET的拓扑动态会在有限带宽上在车辆之间大量传播信息，这加剧了通信通道的拥塞，这是诸如消息丢失，延迟和服务质量下降之类的问题的主要原因。为了减轻这些问题，需要将拥塞检测和控制技术结合到车辆网络中。拥塞控制方法可以是基于拥塞前或拥塞后策略的开环或闭环。我们介绍了城市和公路环境中的车辆通信的一般体系结构，以及对最新的拥塞检测和控制技术的最新调查。我们还确定了现有方法的缺点，并根据不同的分层方案对其进行了分类。通过广泛的文献综述，我们推荐用于解决车辆通讯拥堵的解决方案方法和未来方向。