# The Car-Following Model and Its Applications in the V2X Environment: A Historical Review
## 1 Introduction  
Traffic accidents and congestion are common problems for both those who manage and use transportation systems. Further developments in technology will be able to effectively improve the poor state of the present situation. Relevant intelligent transportation system (ITS) technologies that are represented by the V2X have been developing rapidly in the last few years. The V2X is the general name that has been given to a series of technologies that have been developed, are developing, and will be developed, which are currently represented by Dedicated Short-Range Communication (DSRC)-based and Cellular Network-based technologies, i.e., the C-V2X. V2X technologies enable a vehicle to exchange information with the other elements that are involved in the system, providing the basis for intellectualization. These technologies have been regarded as being an effective way to solve problems such as traffic accidents, congestion and pollution. The information level of transportation systems has been greatly improved with the application of V2X technology, which has made the present-day traffic environment different from that of the past. Information is the basis of decision making. In the V2X environment, the driver-vehicle unit can obtain massive amounts of traffic information and understand the trafficsituation more comprehensively. Based on this better understanding, car-following behavior can be optimized. Thus, the characteristics of car-following behavior and traffic flow, which is the macroscopic result of microcosmic car-following behavior, are significantly different from the previous traffic environment without V2X technology. In the traditional car-following models, only the dual-vehicle interaction between the object vehicle and its preceding vehicle was considered. This defect means that these models cannot be directly employed to describe the car-following behavior in the V2X environment, nor can they be implemented to form the theoretical basis for the analysis of traffic flow characteristics or for the estimation of vehicle energy consumption and its emission. Under these conditions, car-following models need to be further extended or updated.  
Considering these limitations, studies conducted on the car-following model and its applications in the V2X environment were comprehensively reviewed in this paper in order to provide a reference for further exploration. The review that is presented in this paper is organized into three parts:  
* An introduction of the development process of traditional car-following models;
* A description of the current status of research on the car-following model and its applications in the V2X environment;
* A discussion of the achievements and shortcomings of the previous studies along with future research trends.  
The framework of the review that is provided in this paper is as shown in Figure 1.  
The following contents of this paper are organized as follows: the development process of traditional car-following models is introduced in Section 2; the studies on the car-following model and its applications in the V2X environment are reviewed in Section 3; the achievements, shortcomings, and the trends that require further exploration are discussed in Section 4; the conclusion is given in Section 5.