# Usage of V2X Applications in Road Tunnels
## 5 Discussion  
From the research, but also from the testing and analysis, the results indicate that a loss of V2X communication may occur in the tunnels. Tunnels are equipped with a wide range of technologies and devices, but the availability of GNSS is still not sufficient. There are many approaches on how to supplement it, such as an example with the tested scenario. The problem with these complementary solutions and techniques consists of the fact that the position and time accuracy vary and are not centralized, unlike with the solutions based on the GNSS signals. It may occur that each application will work in a different way, and will compute the position and time with a lack of accuracy compared to the others. Each application will work within the particular solution but with a unique error, and thus each vehicle could compute different latitude and longitude while both are at the same place. In the case of V2X communication, it does not work properly when vehicle positions are decentralized, especially in use cases where the position and time validity of the event are crucial. This is specifically related to \"moving\" events, such as slow vehicles, maintenance, and service spreader vehicles on roads, but even more so in use cases such as approaching emergency vehicles, emergency electronic brake light, platooning, etc., where the validity of time is very short, and the position must be precise. The result of the evaluation also showed that communication over the cellular network might be more efficient with regard to the dissemination of the provided information. Especially in the case of V2X communication in the tunnel and its surroundings, where the possibility to change the path, or stop the vehicle, etc., is not possible, the cellular approach could be more efficient, and it could provide information in larger areas. It is also presumable that local microwave V2X communication over ITS-G5 will be worse in normal traffic flow in the tunnel due to the space being filled by other cars. Using hybrid communication, it is possible to share the data and integrate them into the tunnel control system, as well as the city traffic control management system [44], and thus it is possible to plan, schedule, and control these systems as a project with defined processes regarding risk management and decision-making solutions [45]. As part of the design and use of C-ITS in the tunnel, it is possible to implement other future plans and recommendations for tunnel construction and its development. In the tunnel, the data transmission and distribution of information could be carried out directly to the vehicle about the status of the tunnel itself, and about the particular parts such as variable message signs, speed limit, etc., but the tunnel could also obtain information from the vehicle. Examples of data and information from the vehicle and the tunnel infrastructure are as follows:  
* Travel time in the monitored section
* Average speed (section speed)
* Travel time delay in the monitored section
* Detection of a traffic jam in the monitored section
* Detection of a braking/stopped vehicle and direction of vehicle movement
* Vehicle acceleration/deceleration
* Use of vehicle control units
* Number of people in the vehicle (for evacuation modeling)
* In-vehicle infrastructure information (speed limits, delay information)
* Approaching emergency vehicle position in the tunnel
* Position of accident, stationary vehicle, or cargo
* Information about hazardous event/position in tunnels, evacuation information, etc. * Information for drivers in convoys, information about approaching IRS vehicles
* Vehicle maintenance position to prevent potential collisions and emergency lane closures  
This article focused not only on C-ITS communication between vehicles using LTE and ITS-G5, but also in connection with the functions of complex tunnel infrastructure, which is very large.