# Research on Safe Following Distance on an Expressway Based on Braking Process Analysis
## 5 Conclusions  
In this study, according to the characteristics of safe driving and rear-end accidents on expressways, the safe following distance on an expressway is studied from the angle of vehicle braking deceleration based on kinematic principles. Based on the characteristics of the vehicle braking process, three kinds of highway safe following distance models based on braking deceleration were constructed. Based on the investigation of the road section and the study of the calculation model and parameters of the safe following distance, the key parameters of the safe following distance model, such as the driving speed and the deceleration speed and different slope values, were discussed in depth, and the recommended values of the safe following distance of the vehicles on plain and longitudinal slopes were  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{\(V_{r}=V_{B}-V_{A}=20\) km/h} & \multicolumn{4}{c}{**Coefficient of Road Adhesion \(\varphi\)**} & \multicolumn{1}{c}{\(V_{B}\)} \\ \cline{2-6}  & **0.5** & **0.6** & **0.7** & **0.8** & **(km/h)** \\ \hline
**The basic safety distance** & 54.5361 & 50.8616 & 48.2369 & 46.2684 & 80 \\
**between cars** & 68.0576 & 63.3332 & 59.9586 & 57.4276 & 100 \\
**\(D_{2}\) (m)** & 81.5790 & 75.8047 & 71.6802 & 68.5869 & 120 \\ \hline \hline \end{tabular}
\end{table}
Table 11: The basic following distance based on \(V_{B}\) between 60 and 120 km/h when \(i\) = 0, \(V_{r}=20\) km/h.  
Figure 12: Changes in the basic following distance with \(V_{B}\) and \(\varphi\) when \(i\) = 0, \(V_{r}=20\) km/h.  
put forward. The research results show that the calculation results of the safe following distance conform to the requirements of safe following distance in the Implementation Regulations of the Road Traffic Safety Law of the People's Republic of China. The calculation of three kinds of safe following distance can provide a theoretical basis and practical examples for the traffic police department to formulate different traffic management policies. The results of this study have practical guiding significance for improving the vehicle density and transportation efficiency of expressways and reducing the incidence of rear-end traffic accidents on expressways. The next step of this study is to carry out the following research contents:  
1. Construct the calculation model of expressway parking sight distance based on braking deceleration and study the relationship between safe following distance and stopping sight distance.
2. Propose the suggested value of expressway stopping sight distance based on braking deceleration under different longitudinal slopes and study different design speeds.
3. Carry out the vehicle braking deceleration test, to further improve the parameter value of the model and enhance the application value of the research.  
Conceptualization, X.W. and S.F.; Methodology, X.W.; Software, X.W. and S.F.; Validation, X.W. and S.F.; Formal analysis, S.F.; Resources, X.W.; Data curation, X.W. and S.F.; Writing--original draft preparation, X.W. and S.F.; Writing--review and editing, S.F.; Supervision, X.W.; Project administration, X.W. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (grant Nos. 11772277, 51305372); the Open Fund Project of Transportation Infrastructure Intelligent Management and Maintenance Engineering Technology Center of Xiamen City (grant No. TCIMI201803); and the Project of 2011 Collaborative Innovation Center of Fujian Province (grant No. 2016 BJC019).  
Not applicable.  
The authors declare no conflict of interest.