## 3 _Pbc_ Analysis Method and Result
### Scenario Design  
The experimental scenario was designed for independent effect analysis for each element. The selected effect measures for effect analysis of FCW were as follows: cognitive reaction time (s), deceleration from the start of the breaking until the end of breaking (m/s\({}^{2}\)), and number of collisions with the front vehicle (times) as shown in Figure 3.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**TPB Factors** & **Analysis Contents** & **Measure of Effectiveness** & **Analysis Data** \\ \hline \multirow{3}{*}{_PBC_} & Estimation of instantaneous effects in & \multirow{3}{*}{Cognitive reaction time, deceleration, collision} & Four scenario driving results for \\  & collision risk situations using & & each participant (total of 70 people) \\  & virtual simulation & & Daily IoT log data from September \\  & & & 2017–August 2018 \\ \multirow{3}{*}{_ATB_} & Estimation of the number of changes & \multirow{3}{*}{Number of forward collision warnings} & (for forecasting) \\  & in dangerous driving behaviors & & Annual log statistical data from \\  & & & September 2018–August 2020 \\ \multirow{3}{*}{_ATB_} & \multirow{3}{*}{Estimation of the number of changes } & \multirow{3}{*}{Number of forward collision warnings} & (for verification) \\  & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Analysis contents and data for each TPB factor.  
Figure 2: Driving Simulator used in the experiment.  
At the start of the scenario, the study participants drove on a road with a speed limit of 50 km/h, and the driving lane was maintained on the second lane. The reason why the speed limit was selected as 50 km/h was to be the same as the speed limit on the roads in Seoul where the study participants normally drive. The Seoul Metropolitan Government has implemented the \"Safety Speed 5030\" that sets the speed limit for roads in the city to 50 km/h for main and auxiliary arterial roads and 30 km/h for collector roads.  
As shown in Figure 4 below, when the distance between the unexpected vehicle and the participant's vehicle becomes 100 m, the unexpected vehicle changes lanes from the first lane to the second lane (Step 1). The unexpected vehicle accelerates slowly at 0.41 m/s\({}^{2}\) until it reaches a safe distance of 50 m after 15 s of the lane change. After completion of acceleration there is a hold time of 5 s (Step 2). The safety distance of 50 m was calculated based on the driver's cognitive reaction time. For the cognitive response time, the 85 th percentile driver value of 2.5 s is applied, but in an unexpected event, the cognitive response time increases by 35% [22]. By applying a cognitive reaction time of 3.5 s, a safe distance of 50 m at a driving speed of 50 km/h was set. As the length of the safety distance increases, the number of collisions decreases. If the safety distance is short, unnecessary deceleration of the driver occurs before an unexpected situation occurs, which may affect the overall experimental results (cognitive reaction time, deceleration, number of collisions). The safety distance was selected with a leisurely 50 m based on the 85 th percentile driver value.  
Figure 4: Driving simulation scenario.  
Figure 3: The measure of effectiveness of _PBC_ analysis.  
The unexpected vehicle performs an emergency stop, and the participant's cognitive reaction time, deceleration, and collision status were analyzed at the emergency stop of the unexpected vehicle (Step 3). Scenarios were divided into day/night, and a total of 4 experiments were conducted per study participant when FCW was installed and when FCW was not installed. Weather conditions were based on sunny days, and environmental variables that could affect driving such as weather conditions and road pavement were not considered.