## 3 Materials and Methods
### VR Environment and Equipment  
The identification and design of the main urban run-over scenarios were conducted through a comprehensive retrospective in-depth study of accidents involving VRU in the city of Madrid, Spain. From a database provided by INSIA-UPM, a total of 100 accidents in which a vehicle knocks down a pedestrian have been extracted. Urban roads with more than one lane in each direction of traffic have been chosen. This makes it possible to evaluate the reaction of the pedestrian on different lanes by incorporating restrictions on visibility due to the presence of parked vehicles. Taking into account the INSIA-UPM database, in 80% of the cases the vehicle approaches the pedestrian from the left side, so this will be the configuration modeled in the VR scenarios. In the analyzed database, three types of scenarios were identified: T1, collision at a traffic light regulated crosswalk (28%); T2, collision at a non-traffic light regulated crosswalk (21%), and T3, collision outside a crosswalk (51%). Of these, the first type of scenario is the most significant, since the impact vehicle speed was higher than 40 km/h in most cases, and the risk of death by collision is higher than 50% above this speed [31]. Considering those belonging to class T1 and whose collisions occurred at impact speeds above 40 km/h, the following urban scenarios are identified and modeled in VR (Table 1):  
The reconstruction of the aforementioned scenarios has been carried out using Unity3D software (Figure 2). In this powerful cross-platform development framework, the realistic 3D modeling of the traffic sceneries (including both static and dynamic elements of the streets) has been integrated with modules and elements simulating the traffic logic, the vehicle behavior, and the reproduction of the environmental and boundary conditions to recreate the potential collision situations ([[https://youtu.be/AF0](https://youtu.be/AF0) nYteBRE8]([https://youtu.be/AF0](https://youtu.be/AF0) nYteBRE8), accessed on 15 August 2022). The design process is conducted by merging different data sources, such as online maps, satellite imagery, and photos and videos collected by in situ inspection. The main architectural elements and street furniture are integrated to attain a high level of detail, including buildings, bus shelters, trees, and recycle containers, among others. Close-up photos of the original materials and urban elements have also been used to enhance the user's overall sense of immersion with the interface and generate an environment with a \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Scenario**} & **Street Lane for VR** & **Side from Which the** & **GPS Coordinates** \\  & **Collision Point** & **Vehicle Appears** & \\ \hline
**Av. de los Toreros (SC1)** & First & Left & 40\({}^{\circ}\)25\({}^{\prime}\)54.8” N 3\({}^{\circ}\)39\({}^{\prime}\)41.8” W \\ \hline
**Av. Machupichu (SC2)** & Second & Left & 40\({}^{\circ}\)27\({}^{\prime}\)38.6” N 3\({}^{\circ}\)37\({}^{\prime}\)57.7” W \\ \hline
**Calle Hermanos Garcia** & Third & Left & 40\({}^{\circ}\)25\({}^{\prime}\)47.7” N 3\({}^{\circ}\)37\({}^{\prime}\)56.3” W \\
**Noblejas (SC3)** & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Scenarios modeled in VR for the experimental session. Figure 2: A 3D reconstruction of collision scenarios. From left to right: SC1, SC2, and SC3 (Madrid, Spain). level of detail close to reality. Additionally, stereophonic sounds have also been included to reproduce the typical background noise in the streets, such as the environmental noise due to motorized traffic and other users interacting on the pavement and the road, as well as the sound of the engine, tires rolling, and hard braking during the accident simulation. To reproduce the movement of traffic vehicles and pedestrians walking on the side-walks or crossing the road, the corresponding dynamic elements have been mathematically designed and integrated through a simple kinematic model to replicate their motion and trajectories.