# Publish/Subscribe-Middleware-Based Intelligent Transportation Systems: Applications and Challenges
## 7 Conclusions  
ITS applies advanced information and communication technologies to transportation networks to improve safety, efficiency, and sustainability. The ARC-IT reference architecture provides a structured framework for ITS design, comprising the Enterprise, Functional, Physical, and Communications Views. The Communications View defines the protocols and standards that enable data exchange between system components. This review focused on the Communications View of ARC-IT v9.3, investigating the role of publish/subscribe middleware in improving ITS performance. Given the limited number of studies addressing this intersection explicitly, our goal was to consolidate knowledge on middleware-based communication models, identify application domains across computer network infrastructure, transportation modes, and communication technologies, and highlight key challenges. The findings aim to guide researchers and practitioners toward building scalable, interoperable, and real-time communication solutions for next-generation ITS. This study found that publish/subscribe middleware provides clear benefits in several ITS application areas, especially those requiring real-time communication and dynamic scalability. For example, COPSS demonstrated high value in VANET scenarios involving safety-critical alerts, outperforming traditional broadcast and polling methods in efficiency and reliability. Apache Kafka is highly scalable and effective for high-throughput event streaming in IoT-based traffic surveillance, though it requires significant computational resources. DDS middleware has shown strong real-time and reliability capabilities in structured environments like railway systems and autonomous vehicle communication, but its configuration can be complex. Conversely, protocols such as MQTT are easy to deploy but are less suitable for mission-critical or high-density scenarios. XMPP-based participatory sensing and IMS Presence Services offer practical public transportation and fleet monitoring solutions but face scalability and data accuracy challenges. These findings indicate that the choice of middleware for ITS applications is influenced by system requirements, the availability of infrastructure, and performance limitations. Therefore, there is a strong need for hybrid approaches that combine the adaptability of custom middleware with the robustness of standardized platforms to ensure cost-effective, secure, and scalable ITS deployments. Additional challenges in integrating publish/subscribe middleware in ITS include privacy risks from crowdsensing and data sharing, real-time data processing constraints, fault tolerance, and system heterogeneity, connectivity issues due to bandwidth limits and mobility, and security vulnerabilities such as unauthorized data access, broker attacks, and protocol misconfigurations. Overcoming these barriers is crucial for developing secure, scalable, and interoperable ITS solutions. **Author Contributions:** Conceptualization, B.A. ; methodology, F.A. ; validation, F.A. and E.A.-N.; formal analysis, E.H. and R.R.A. ; investigation, E.H. and R.R.A. ; resources, F.A., E.H., and R.R.A. ; data curation, E.H. and R.R.A. ; writing--original draft preparation, E.H., R.R.A., and F.A. ; writing--review and editing, F.A. and E.A.-N.; visualization, F.A., E.H. and R.R.A. ; supervision, B.A. ; project administration, B.A. ; funding acquisition, B.A. All authors have read and agreed to the published version of the manuscript. **Funding:** The APC was funded by the Deanship of Research Oversight and Coordination (DROC), King Fahd University of Petroleum & Minerals (KFUPM). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Not applicable. **Acknowledgments:** The authors would like to acknowledge all support provided by Alfozan Academy, the Center for Excellence in Development of Nonprofit Organizations (CEDNPO), and KFUPM. **Conflicts of Interest:** The authors declare no conflicts of interest.