## 3 Travel Speed Volatility
### Analysis of Travel Speed Volatility
#### 3.2.1 Travel Speed Volatility at Morning Peak  
According to the current Chinese code \"Urban road traffic performance index (DB11/T 785--2011)\" [17] and \"Evaluation methods for road traffic congestion levels (GA/T 115--2020)\" [18], urban expressway traffic status is defined as four categories based on average travel speed, as shown in Table 2. The data showed that the traffic status of most road sections of the Beijing 3 rd Ring Road was that of light congestion during the weekday morning peak and the road sections had a wide travel speed fluctuation range. The average travel speed of more than 75% of the road sections was lower than 50 km/h, as shown in Figure 4(a). The maximum travel speed of more than 92% of the road sections was more than 50 km/h, the minimum travel speed of the road sections was 30 km/h, and the travel speed range of more than 92% of the road sections was larger than 50 km/h during the weekday morning peak, as shown in Figure 4(b). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Characteristics** & \multicolumn{3}{c}{**Characterization of Travel Speed Fluctuations**} \\ \hline Similarity & \(\bullet\) & Cyclicity: The average travel speed of the road sections was different during the weekday morning peak from month to month, the average travel speed of the road sections significantly decreased during the weekday morning peak after students back to school in September. \\  & \(\bullet\) & Time variability: During the weekday morning peak, as the departure time was delayed, the average travel speed fluctuation basically showed that it first decreased and then increased, and the fluctuation trend of the average travel speed on different road sections stayed the same. \\  & \(\bullet\) & Large-scale volatility: The travel speed range at 10 min intervals of more than 85% of the road sections was larger than 20 km/h in more than 90% of periods, and the travel speed range was large. \\  & \(\bullet\) & Light congestion: The average travel speed of more than 75% of the road sections was lower than 50 km/h during the weekday morning peak, and the travel speed showed that the traffic status was that of light congestion. \\ \hline Specificity & \(\bullet\) & Different: Different road sections had different traffic statuses and different magnitudes of travel speed cyclicity reductions during the same periods. \\  & \(\bullet\) & Counter-cyclicity: Very few road sections showed counter-cyclicity of travel speed in some periods. The average travel speed of a few of the road sections showed an increase rather than a decrease in some periods after the students back to school. \\  & \(\bullet\) & Non-transmissive: Due to the high density of entrances and exits on the Beijing 3 rd Ring Road, there was no significant transitivity and lag in travel speed between adjacent road sections. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The travel speed volatility characteristics of Beijing 3 rd Ring Road sections. Figure 5: Average, maximum, and minimum of the travel speed of the Beijing 3 rd Ring Road: (**a**) average travel speed and reduction ratio; (**b**) maximum and minimum of travel speed. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Traffic Status** & **Smooth** & \begin{tabular}{c} **Light** \\ **Congestion** \\ \end{tabular} & \
\begin{tabular}{c} **Medium** \\ **Congestion** \\ \end{tabular} &
\begin{tabular}{c} **Severe** \\ **Congestion** \\ \end{tabular} \\ \hline Average travel speed \(\overline{v}\)\({}^{*}\) (km/h) & \(\overline{v}\geq 50\) & \(35\leq\overline{v}<50\) & \(20\leq\overline{v}<35\) & \(0\leq\overline{v}<20\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Urban expressway section traffic status definition.