# Usage of V2X Applications in Road Tunnels
## 1 Introduction
Within the research, it was found that the positioning of vehicles in vehicular ad hoc networks (VANETs) is crucial, as well as for the purposes of communication between cars and infrastructure. In normal operation of C-ITS (Cooperative-Intelligent Transport Systems), GNSS-based localization is mainly used. However, in tunnels, the GNSS is limited or unavailable. The proposed research strategies are presented in several articles, for example, New Roadside Units (RSU) Positioning [16] by [PERSON], which presents a specific positioning approach that could be used for vehicular communication. However, there are no specifics mentioned for tunnels, and in addition, the RSU also requires GNSS as well as on-board units placed in the cars. Similar work [17] is presented by [PERSON] et al., where the tunnels are considered. The simulated numerical results show the possible improvements for V2X communication. In [PERSON]'s article [18], the RFID-assisted approach is presented, and then the Matlab simulation is established. In [PERSON]'s article [19], the fusion model of GPS (Global Positioning System) and non-GPS systems is presented with an emphasis on VANETs. However, the results only show the output of the simulation tool. For this reason, the experimental analysis of V2X communication based on assisted localization methods was performed under real conditions and is presented in the article. The main goal of the experiment is to verify whether V2X communication could be possible under the conditions using assisted localization methods in the limited GNSS availability environment, for example, in the road tunnel, where V2X communication is very important, especially from a safety point of view. The unique experimental test was carried out in the Blanka tunnel complex in Prague, because the tunnel is long enough to completely lose the GNSS signal (more than 5 km, which is vertically and horizontally divided and contains several intersections directly in the tunnel) and the verification of the C-ITS communication could be applied there. Within the test, the validity of C-ITS messages was constantly verified using the unique V2X software stack adopted in the testing units, so the invalid messages are ignored according to the ETSI standards, e.g., because of the positioning accuracy, and thus the V2X messages are not displayed in the application. The uniqueness of the whole experiment lies in the fact that the tunnel was closed, which also enabled the testing of standardized scenarios of V2X communication directly in the tunnel, for example, a stationary vehicle use case in the tunnel, which would not be possible during normal operation with real traffic. Experience and needs with tunnel technology in Prague were also taken into account in the most common use cases related to tunnel emergencies. The most common case of extraordinary events is the stationary vehicle (failure, accident, etc.) that evokes the closure of a tunnel or a lane in the tunnel. Another common phenomenon is the emergency vehicles of the police, fire brigade, ambulance, or the intervention of a service vehicle in the tunnel, which also leads to the closure, or restriction of traffic in the tunnel at least. Due to the length of the Blanka tunnel and the junctions inside, the case of a stationary vehicle is the appropriate one for using the precise location, which fails via GNSS-based positioning, that is commonly used in the field of C-ITS and other smart applications. Therefore, the unique C-ITS testing was performed in the tunnel, where positioning was ensured by assisted localization approaches based on Dead Reckoning. The test results may benefit the subsequent operation of C-ITS in places where GNSS availability is limited. Therefore, the pilot test and its methodology were designed with a focus on the verification of whether the C-ITS is applicable and usable in the tunnel, and if so, further testing could be performed in a real traffic scenario with normal traffic flow.