# The Car-Following Model and Its Applications in the V2X Environment: A Historical Review
## 4 Discussion
### Research Trends  
Incorporating the Development Laws of V2X Technology  
The development of things is a process. As the application of emerging information technologies in transportation systems, V2X technology cannot achieve its development overnight. However, the penetration and reliability of V2X technology were assumed as 100% in most of the previous studies, which deviates from the objective development laws of things. To further develop and enrich the traffic flow, it is necessary to incorporate the penetration and the reliability of V2X technology in future research on car-following behavior. Specifically, further works should pay more attention to the impacts of various V2X technologies and the penetration/reliability/performance/availability of the devices on car-following behavior and traffic flow in the different development stages of the V2X environment. Considering the Driver/Vehicle Attribute in Modeling Car-following Behavior  
The drivers' car-following behavior is essentially the implementation of their subjective driving will, and the vehicle is the specific carrier to implement the will. Thus, the attributes of driver and vehicle will exert significant impacts on car-following behavior. To be specific, drivers with different attributes may exhibit different car-following behavior under the same conditions, and the same driver may also exhibit different car-following behavior under the same conditions when driving vehicles with different attributes. In addition to the attributes of the object vehicle and its driver, the attributes of other vehicles and their drivers will also impact the car-following behavior of the object vehicle, which has been confirmed in several previous studies. In the V2X environment, it is possible to collect and exchange information about the attributes of the connected vehicles in the system and their drivers. However, the impacts of this kind of information have not been explored. Considering that the automatic controller cannot fully replace the human driver in the foreseeable future, it is necessary to conduct research on the impacts of the attributes of the vehicles and their drivers on car-following behavior and traffic flow in the V2X environment. Comprehensively Incorporating the Various Information Sources  
It is very limited for human drivers to obtain information by relying on themselves. However, in the V2X environment, the driver can theoretically obtain information on all vehicles in the system by utilizing the relevant devices. However, the exploration of the impacts of different information on car-following behavior and traffic flow in the previous works is isolated. Thus, it is necessary to discuss these impacts comprehensively and comparatively. Based on this, the impacts of various information sources and their aggregation on car-following behavior and traffic flow under different conditions can be analyzed. Further considering the limitation of a driver's energy and attention, personalized information schemes can be established for different drivers under different conditions, which has significance for the development of V2X technology. Focus on the Car-following Behavior Mechanism Affected by Various Information Sources  
The majority of attention in the previous works was paid to the external characteristics of car-following behavior, although the extended/improved models based on the traditional car-following models such as the FVD model can describe the car-following behavior characteristics under special conditions with considerable high accuracy. The nature, i.e., the internal mechanism, of car-following behavior has not received enough attention. Human behavior, including that of car-following, is the result of the interaction of the person's internal subjective will, emotion, personality, and other factors. \"All conscious actions of human beings are to enhance their own happiness and satisfaction\", as pointed out by [PERSON].