# Usage of V2X Applications in Road Tunnels
## 4 Results  
Analysis of V2X communication in the tunnel environment showed several outputs and results. Firstly, LTE connectivity had been available throughout the test, regardless of whether the equipped vehicle was placed in the tunnel or outside. The LTE coverage was sufficient, and the C-ITS messages from the backend were captured throughout the Blanka tunnel. However, the visualization of results was influenced by the positioning error, which occurred after 3 km from the tunnel entrance (see Figure 6). The testing direction was from southwest to northeast. The pre-test showed that the positioning error was growing with the length of the testing range. However, the position in front of the tunnel was relatively correct, and thus the major test could be performed. During the major test, it turned out that the OBUs were communicating with each other. The OBUs correctly (at least sufficiently for the V2X commutation) computed their own position even though the GNSS signal was not available. It was also possible to observe on the HMI that the C-ITS messages were valid, and that the information was displayed on the mobile app when the arriving vehicle was closer to the stationary vehicle. This means that both OBUs calculated the time and position in the same way. The testing showed that the OBUs are prepared for unexpected circumstances also in the tunnel, and it is possible to disseminate information, for example, about the stationary vehicle in the tunnel. A visualization of the information is shown in Figure 7, and the mobile app also provided a relatively correct estimate of the distance between vehicles. However, the output showed that the position and time updates were limited. During the test, the display of information was not continuous, and the information about the distance changed in unexpected steps compared to the knowledge of the proper system working under standard environmental conditions. Sometimes,  
Figure 6: Captured C-ITS messages from the backend over LTE. HMI disappeared for a while, which probably means that the position was inaccurate (unavailable) at that moment. Based on the processed data from the C-ITS communication, it is quite clear that the communication over ITS-G5 was limited. However, the results showed that line of sight is not necessary for communication and that the signal from the transmitter sufficiently bounced off the tunnel walls. On the other hand, the signal was receivable only in the closer surroundings before the tunnel entrance. From the data log, it follows that the communication range was hundreds of meters (see Figure 8). It is necessary to keep in mind that each tunnel is specific and different, so the conditions of V2X communication may also be completely different. Quite a positive result was also found for packet delivery, where it was possible to observe that a similar number of messages were captured over ITS-G5 as over LTE. From Figure 8, it can be seen that a lack of communication occurred while the arriving vehicle was entering the tunnel tube. This is probably due to the recovery of the system after the unavailability of GNSS. This could be a crucial part of communication, because the arriving vehicle could not know when the GNSS was exactly lost and when the procedure of positioning based on the 3D accelerator should be applied. However, the vehicles were connected when the direct distance was not guaranteed, probably due to signal reflections on the tunnel wall. The fact that the tunnel was empty,  
Figure 8: Captured C-ITS messages in terms of distance from the stationary vehicle. Figure 7: Testing of the V2X scenario (stationary vehicle) in the Blanka tunnel. without vehicles that would normally be passing, should also be taken into account, because the conditions during the test were specific. In Figure 9, the position of the arriving vehicle (when the C-ITS message was received) is shown on the map, as well as the position of the stationary vehicle.