# Assessing Traffic-Flow Safety at Various Levels of Autonomous-Vehicle Market Penetration
## 3 Methodology
### Human-Driving Vehicles (HDVs) Input Variable Estimation  
#### 3.4.1 VISSIM Input Variable and Range Setting  
To simulate the driving behavior of a car, it is necessary to adjust various input variables, but it is difficult to derive the optimal values of all variables. Therefore, in this study, after reviewing the existing studies that calibrated the input variables of general vehicles using VISSIM, the main input variables that have the greatest influence on the driving behavior of a vehicle and the minimum and maximum values of each variable were selected as shown in Table 1. The range values of the input variables were selected within the range of the minimum and maximum values of each input variable in the existing studies.  
Among the input variables of the vehicle-following model, CC0, CC1, and CC2 were selected as the input variables that affect the longitudinal motion. Figure 2 illustrates the concepts of CC0 (standstill distance), CC1 (headway time), and CC2 (car-following distance). CC0 (standstill distance) is the minimum distance that a vehicle must maintain when stopped in order to maintain a safe distance from other vehicles. CC1 (headway time) is the amount of headway the car wants to maintain with the car in front of it. CC2 (car-following distance) is the safe following distance (CC0 + CC1 \(\times\) vehicle speed) plus an additional buffer.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Stakeholders** & **[PERSON] et al.** & **[PERSON] et al.** & **[PERSON] et al.** & **[PERSON] et al.** & **[PERSON] (2022) [24]** & **This Study** \\  & **(2006)**[13] & **(2018)**[15] & **(2023)**[16] & **(2017)**[23] & **[PERSON] (2022)**[24] & **This Study** \\ \hline \hline   CCO, Standstill distance (m) & 1.0–2.0 & 2.23–6.07 & 0.0–3.0 & 0.5–1.5 & 0.0–20.0 & 0.0–3.0 \\   CC1, Headway time (s) & 0.5–3.0 & 0.0–16.9 & 0.0–2.0 & 0.5–1.5 & 0.0–5.0 & 0.0–5.0 \\   CC2, Car-following distance & 0.0–15.0 & 2.23–20.94 & 0.0–40.0 & 2.0–10.0 & 0.0–10.0 & 0.0–40.0 \\  (m) & \(-\)30.0–0.0 & - & - & - & \(-\)20.0–0.0 & - \\   CC3, Threshold for entering & \(-\)30.0–0.0 & - & - & - & \(-\)20.0–0.0 & - \\   following (s) & \(-\)1.0–0.0 & - & - & - & \(-\)5.0–0.0 & - \\   CC4, Negative following & \(-\)1.0–0.0 & - & - & - & \(-\)5.0–0.0 & - \\   threshold (m/s) & 0.0–1.0 & - & - & - & 0.1–5.0 & - \\   CC6, Speed dependency of & \(-\)20.0 & - & - & - & 0.1–20.0 & - \\   oscillation (1/(m/s)) & 0.0–1.0 & - & - & - & \(-\)1.0–1.0 & - \\   CC7, Oscillation during & \(-\)1.0–8.0 & - & - & - & 0.0–8.0 & - \\   acceleration (m/s\({}^{2}\)) & 1.0–8.0 & - & - & - & 0.0–8.0 & - \\   CC9, Acceleration & \(-\)3.0 & - & - & - & 0.0–8.0 & - \\  80 km/h (m/s\({}^{2}\)) & 200–300 & - & - & - & 72–108 & - \\   Look-ahead distance & 1–5 & - & - & - & - & - \\   Observed vehicles & \(-\)3.0–0.2 & - & - & - & - & - \\   Accepted deceleration & \(-\)3.0–0.2 & - & - & - & - & - \\  (m/s\({}^{2}\)) & 0.1–0.9 & - & - & - & - & - \\   LC4, Minimum headway (m) & 0.1–0.9 & - & - & - & - & - \\   Maximum deceleration for & \(-\)5.0–\(-\)1.0 & - & \(-\)9.0–0.0 & - & - & \(-\)5.0–0.0 \\   cooperative braking (m/s\({}^{2}\)) & \(-\)5.0–\(-\)1.0 & - & 0.0–1.0 & - & - & 0.0–1.0 \\   Safety-distance & - & - & 0.0–1.0 & - & - & 0.0–1.0 \\   reduction factor & & & & & & \\ \hline \hline  & & & & & & \\ \end{tabular}
\end{table}
Table 1: Driving behavior parameter range for VISSIM calibration.  
Maximum deceleration for cooperative braking and safety-distance reduction factor were selected as the input variables with the greatest influence on lateral movement. Maximum deceleration for cooperative braking is the maximum deceleration of the vehicle when changing lanes, and the safety-distance reduction factor is the percentage of the safety distance that is reduced when changing lanes. During the analysis, all but five of the input variables were set to their default values in VISSIM.