## 3 Methodology Applied in This Research  
Figure 1 presents the research flow of this study for the driving phobia VRET design and development. The project formulation made at the beginning was to decide how to implement the research, perform risk assessment, and hypothesize expected results. Literature related to VRET, driving phobia, CBT, and PTSD were reviewed and referenced before designing the exposure treatment scenario. The virtual reality immersive environments were constructed to model different fear levels of scenarios. The constructed VRET prototype has been examined by psychologists and an iterative modification process was executed until the psychologists were confident that the system matched the needs of ethical and medically acceptable driving phobia treatments.  
Figure 1: The research flow of the virtual reality-based exposure therapy (VRET) system design and development.  
The VRET system is constructed using a seven-level exposure therapy design as shown in Figure 2. Since some patients are extremely afraid of car crashes, pedestrians and other driving vehicles do not appear in the immersive environment for the initial test runs. All of the simulation scenes follow a single route map. Subjects drive a specified distance to reach a destination before advancing to a higher level. Each level has its unique simulation environment, time, and treatment objectives. The details of each level are highlighted as follows.  
1. Driving in the suburbs during the daytime, the speed limit is 40 km/h.
2. Driving in the suburbs at night, the speed limit is 40 km/h.
3. Driving on the highway during the daytime, the speed limit is 110 km/h, and the system will ask subjects to drive faster if the driving speed is less than 90 km/h.
4. Driving on the highway at night, the speed limit is 110 km/h, and the system will ask subjects to drive faster if the driving speed is less than 90 km/h.
5. Driving on the highway at night, the speed limit is 110 km/h, and the system will ask subjects to drive faster if the driving speed is less than 90 km/h. Subjects will be expected to traverse a tunnel.
6. Driving on a mountain road during the daytime, the speed limit is 50 km/h.
7. Driving on the mountain road at night, the speed limit is 50 km/h.  
The VRET experiment flow is illustrated in Figure 3. The treatment begins with a detailed introduction about the experimental objective, method, procedure, expected risk, and relevant disclaimer information. A pre-test questionnaire is completed by the subject before the experiment to measure the subject's mental state. The questionnaire asks about the subject's behavior, thoughts, and emotions in regard to previous driving experiences. During the experiment, bio-data including heart rate, skin conductance, body temperature, respiration, and head movement are recorded in the computer database for statistical analysis. If virtual reality vertigo or other motion sickness symptoms occur to the subject during the VRET session, an emergency stop is triggered and the experiment is terminated. After the immersive treatment is finished, subjects are asked to complete a post-test feedback form.  
Figure 2: Scenario design level chart.  
A total of thirty-one subjects including 14 males and 17 females at the university participated in the pre-test of the VRET prototype. The inclusion criteria are aged between 20 and 25 years old, possession of a valid driving license, and described a fear of at least one type of driving phobias such as driving on highways, mountain roads, or congested traffic.