# Safe Driving Distance and Speed for Collision Avoidance in Connected Vehicles
## 4 Stopping Distance and Braking Dynamics
For example, at 100 km/h, the total stopping distance on dry and wet asphalt is 71 m and 84 m, respectively, yielding an extra stopping distance of 13 m. Moreover, the extra stopping distance at 150 km/h is 30 m.  
The extra stopping distance in meters on snowy roads compared to dry asphalt roads for different speeds is presented in Figure 10. For example, at 30 km/h, the stopping distance of a vehicle traveling on dry asphalt is 12.2 m compared to 26.0 m on a snowy road at the same speed by the same vehicle. That is 13.8 m extra stopping distance (more than the stopping distance in dry asphalt). Moreover, the extra stopping distance is even more at 150 km/h, where the stopping distance on dry asphalt is 138 m, compared to 484 m on a snowy road (a considerable difference of 346 m, an increase in extra stopping distance of more than 250%). Figure 8: Effect of the tire state on the braking distance. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline
**Speed** & **10** & **20** & **30** & **40** & **50** & **60** & **70** & **80** & **90** & **100** & **110** & **120** & **130** & **140** & **150** \\ \hline Asphalt (Wet) & 3.2 & 7.3 & 12.2 & 18 & 25 & 32 & 40 & 50 & 60 & 71 & 82 & 95 & 108 & 123 & 138 \\ Pavement & 3.3 & 7.8 & 13.4 & 20 & 28 & 37 & 47 & 58 & 71 & 84 & 99 & 114 & 131 & 149 & 168 \\ Pavement & 3.3 & 7.5 & 12.8 & 19 & 26 & 34 & 44 & 54 & 65 & 77 & 90 & 104 & 119 & 135 & 152 \\ Pavement & 3.4 & 8.2 & 14.2 & 22 & 30 & 40 & 52 & 64 & 78 & 93 & 110 & 128 & 147 & 167 & 189 \\ Snowy & 4.7 & 13.4 & 26.0 & 43 & 63 & 87 & 116 & 148 & 184 & 224 & 268 & 316 & 368 & 424 & 484 \\ Ice & 6.7 & 21.3 & 43.7 & 74 & 112 & 158 & 212 & 274 & 344 & 421 & 506 & 600 & 701 & 810 & 927 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Total stopping distance for different road types and for different speeds. In Figure 11, the stopping distance as the sum of reaction distance and braking distance for different speeds on different road types is presented, assuming the reaction time is 1 s assuming the vehicle has new tires. Three cases are shown as:  
CASE A: The stopping distance of a vehicle traveling on dry asphalt road at different speeds as reaction distance plus braking distance. At a low speed (for example, 30 km/h), the reaction distance is doubled when the braking distance 8 m (independent of the type of road), and the braking distance is 4 m. The braking distance becomes higher at high speed (braking distance = 84 m compared to a reaction distance of 39 m at 140 km/h). CASE B: On a snowy road, the stopping distance is longer mainly due to the longer braking distance. At 20 km/h, for example, the braking distance is 58.5% of the stopping distance (7.9 m), and at higher speed, for example, at 140 km/h, the braking distance is 90.8% of the stopping distance (385 m). CASE C: The same phenomenon is observed on icy roads. The braking distance at 20 km/h is 73.7% (15.7 m) of the stopping distance and at a higher speed of 140 km/h, the braking distance is 95.2% of the stopping distance. Figure 10: Extra stopping distance in meters on snow road compared to dry asphalt road for different speeds. Figure 9: Extra stopping distance in meters on wet asphalt road compared to dry asphalt road for different speeds. Table 4 presents the stopping distance (in meters) as the sum of the reaction distance (in meters) and braking distance (in meters) for different road types. As we showed from the previous data obtained, the reaction distance is independent of the road type since the reaction time is the same regardless of the road type the driver is traveling on. Dry asphalt has the least braking distance at the same speed as the other road types, while the icy road has the highest braking distance and hence the highest stopping distance at the same speed. At 20 km/h, the braking distance on dry asphalt is just 1.7 m compared to dry pavement (2.0 m), wet asphalt (2.2 m), wet pavement (2.6 m), snowy road (7.9 m), and Icy road (15.7 m). There is a similar trend even at higher speeds.