# Publish/Subscribe-Middleware-Based Intelligent Transportation Systems: Applications and Challenges
## 1 Introduction
It provides insights for researchers, ITS practitioners, and policymakers who aim to deploy resilient, high-performance communication infrastructures in next-generation ITS. Middleware is software that facilitates communication between various applications or systems and serves as a bridge for efficient data exchange. Operating as a layer of abstraction, it enables applications to communicate without delving into the intricacies of the underlying network or hardware infrastructure [12]. In transportation, as mentioned, middleware facilitates communication and updates between components like vehicles and control systems, providing vital data such as actual vehicle positions, deviations from the static timetable, crowdedness information, etc. [13]. In addition, middleware finds diverse applications, such as data and information management, functioning as a repository for dynamic vehicle environment data within a network. This data encompasses sensor data, information exchanged between vehicles, and static data like digital maps [14]. [PERSON] et al. [12] emphasized the role of middleware in addressing disparate operating systems and the necessity for standardized interfaces, providing a unified platform for application interaction across different operating systems. Additionally, middleware can be deployed in transportation systems, including underground railways, for safety monitoring and control, ensuring efficient data transfer to overcome periodic communication disruptions. As highlighted by [PERSON] et al. [14], middleware is crucial in tackling real-time data processing and analysis challenges. It enables real-time data processing and supports various applications to enhance road safety and efficiency by effectively disseminating and processing real-time data from beacons, supporting flexible queries, and aggregating data flow to provide drivers with timely and accurate information. Utilizing middleware in transportation is considered essential to modern transformations and an important factor in constructing Smart Cities, as it seeks to achieve effective integration between modes of transportation, improve road planning, enhance the traveler experience, improve fleet management, and achieve environmental sustainability. [PERSON] et al. mentioned in their study [14] that publish/subscribe middleware is a type of middleware that simplifies communication between publishers and subscribers in a distributed system. It allows publishers to send messages independently from subscribers, who can express interest in receiving specific message types called topics. Some publish/subscribe systems comprise brokers, which receive messages and subscriptions, filter messages based on subscriptions, and deliver the messages to the appropriate subscribers. Publish/subscribe middleware plays an essential role in transportation by supporting diverse applications. It can provide timely and accurate information about road conditions, accidents, and hazards to drivers, thereby supporting safety applications. Moreover, the asynchronous and one-to-many characteristics of the publish/subscribe system make it more suitable than other communication paradigms [15]. Publish/subscribe middleware is also helpful in managing platoons of vehicles, analyzing traffic patterns and trends, and supporting context-aware applications in transportation. [PERSON] et al. [12] illustrated that publish/subscribe middleware, such as real-time DDS,can be used for on-board applications in the railway domain. It enables disruption-aware communication with the outside network, ensuring efficient real-time data transfer. In general, publish/subscribe middleware offers a flexible and efficient communication mechanism for exchanging information in transportation systems. Employing the publish/subscribe model through middleware enables scalability, flexibility, and responsiveness, making it suitable for dynamic and distributed environments like ITS.