## 3 Travel Speed Volatility
### Analysis of Travel Speed Volatility
#### 3.2.2 Travel Speed Volatility at 10 min Intervals of Morning Peak  
The travel speed volatility indexes (average, standard deviation, maximum, minimum, and range) and travel speed volatility change indexes (the reduction ratio of average travel speed, travel delay per unit of distance based on average travel speed, the reduction in standard deviation, and reduction in travel speed range) of 336 periods of 28 road sections of the Beijing 3 rd Ring Road were analyzed at 10 min intervals during the weekday morning peak. The data showed that the average travel speed of 28 road sections of the Beijing 3 rd Ring Road significantly decreased in most periods (more than 90% share) after the students back to school, with 73%, 54%, 33%, and 18% of 336 periods showing reduction ratios of the average travel speed of 10%, 20%, 30%, and 40%, respectively, and there were three road sections with a reduction ratio of the average travel speed of more than 55% at 10 min intervals. After the students back to school, the average travel speed of nine sections was lower than 20 km/h in 73 periods (about 22% share), the average travel speed of 20 sections was lower than 35 km/h in 186 periods (more than 55% share), and the average travel speed of 28 sections was lower than 50 km/h in 291 periods (about 87% share), as shown in Figure 6. Eight road sections showed a decrease in the average travel speed larger than 20 km/h in 24 periods (more than 7% share), and 22 road sections had a decrease in the average travel speed larger than 10 km/h in 138 periods (more than 41% share) after the students back to school. Figure 6: Average travel speed and reduction ratio of the Beijing 3 rd Ring Road: (**a**) Inner Ring; (**b**) Outer Ring. The greater the travel delay per unit distance based on the average travel speed, the greater the impact of the students back to school on road traffic. After the students back to school, the maximum travel delay per unit distance was larger than 160 s/km, and a large traffic congestion impact was generated, as shown in Figure 7. The data showed that the travel delay per unit distance of 24 road sections was larger than 10 s/km in 234 periods (about 70% share), the travel delay per unit distance of 22 road sections was larger than 20 s/km in 192 periods (more than 57% share), and the travel delay per unit distance of 21 road sections was larger than 30 s/km in 146 periods (more than 43% share). The lower the standard deviation of the travel speed, the smaller the difference between the travel speed and the average travel speed and the more stable the travel speed. The standard deviation of the travel speed of 28 road sections was lower than 20 km/h in 335 periods, the standard deviation of the travel speed of 26 road sections was lower than 10 km/h in more than 193 periods (about 57% share), and the standard deviation of the travel speed of two road sections was lower than 5 km/h in 14 periods (more than 4% share), as shown in Figure 8. After the students back to school, the reduction in the standard deviation of the travel speed of 27 road sections was larger than 0 km/h in 202 periods (more than 60% share), and the reduction in the standard deviation of the travel speed of 25 road sections was larger than 2 km/h in 105 periods (more than 31% share). The maximum and minimum of the travel speed of most road sections were lower than 75 km/h and lower than 35 km/h, respectively, during most periods, as shown in Figure 9. The travel speed range of 24 road sections was larger than 20 km/h in more than 305 periods (more than 90% share), as shown in Figure 10. After the students back to school, the maximum, minimum, and range of the travel speed of most road sections decreased in most periods. The data showed that the reduction in the travel speed range of 26 road sections was larger than 10 km/h in 126 periods (about 38% share) and the reduction in the travel speed range of 27 road sections was larger than 5 km/h in 189 periods (more than 56% share). The lower the travel speed range, the more stable the travel speed.