## 8 Conclusions & Future Directions  
This article has proposed an intelligent hybrid V2X technology selection algorithm by combining the strengths of both short-range and long-range vehicular communication technologies. DSRC, CV2X PC5, and 5G Uu capabilities have been integrated in V2X nodes and the selected KPIs, including one-way end-to-end latency, PDR, and Reliability have been evaluated. A fair experimental analysis of hybrid V2X communications has been conducted in a real-life road environment with two V2X nodes. Through the utilization of our in-house developed CAMINO V2X communication management framework along with the hybrid V2X extensions, we conducted a rigorous assessment of the technologies under uniform conditions. This encompassed various transmission-related parameters such as transmission intervals, packets sizes and simultaneous transmissions from different V2X technologies. Each test iteration was repeated multiple times to guarantee the reproducibility of the results. According to the experimentation results, hybrid V2X technology selection optimizes CAM transmission latency, PDR, and reliability. Although DSRC offers lower latency than C-V2X PC5 and 5G, it has the smallest range in our setup. Contrary to it, C-V2X PC5 has a better range in our experimental setup but it suffers in terms of latency. Intelligently adapting the CAM and DENM transmission frequency in a joint CAM and DENM transmission scenario is shown to proactively minimize the network congestion and degradation of KPIs, especially in dense scenarios. Conducting scalability tests becomes imperative to derive broader conclusions regarding the impact of a high user density environment on the one-way end-to-end latency performance of individual technologies, as well as to assess the influence of DENM messages on technology performance. Nevertheless, executing these tests with real-hardware presents considerable challenges due to the demanding prerequisites, necessitating a substantial number of V2X nodes. Some of the future research directions in this domain include a more scalable implementation, variable number of V2X nodes, and inclusion of further C-ITS message types and their respective use cases. Novel machine learning-based solutions and clustering of V2X nodes could also be explored for hybrid V2X communications. Moreover, LiFi, an interesting technology that can use headlamps of vehicles and/or street lights for communication, could be explored in the context of hybrid V2X communications. The potential use of  
Figure 17: Joint CAM and Decentralized Environmental Notification Message (DENM) transmission scenario using hybrid V2X, (**a**) distance between OBU1 and OBU2, (**b**) observed one-way end-to-end latency for CAMs and DENMs on OBU2, and (**c**) intelligently selected V2X technology on OBU1. NR sidelink considering its unicast capabilities alongside the usual multicast features could be explored. This could be useful for applications such as critical/crisis communication. Conceptualization, I.K., V.M. and D.N. ; methodology, I.K., V.M. and D.N. ; software, I.K., V.M. and D.N. ; validation, I.K. ; formal analysis, I.K. ; investigation, I.K. ; resources, I.K. ; data curation, I.K. ; writing--original draft preparation, I.K. ; writing--review and editing, I.K., V.M., D.N., A.S. and I.M. ; visualization, I.K. ; supervision, I.M. ; project administration, V.M., D.N., A.S. and I.M. ; funding acquisition, D.N., A.S. and I.M. All authors have read and agreed to the published version of the manuscript. This article has received funding from the European H2020 Program under grant agreement 952189 (5G-BLUEPRINT project) and by the Horizon Europe program under the MCSA Staff Exchanges 2021 grant agreement 101086218 (EVOLVE project). The raw data supporting the conclusions of this article will be made available by the authors on request. The authors declare no conflicts of interest.