# The Hyperloop System and Stakeholders: A Review and Future Directions
## 1 Introduction  
The hyperloop is defined as a mode of land transportation capable of high-speed and driverless operations in which a vehicle is guided through a low-pressure tube or system of tubes, for passengers and/or cargo [1]. It is a novel mode of intercity transport, designed to connect cities safely, efficiently, and sustainably, in a fixed guideway tube-based infrastructure. The hyperloop is a mode for passenger and freight transport that travels at ultra-high speeds of up to 1200 km per hour. It may also be described as a pod- and magnetic-levitation-based mode of transport in a low-pressure-sealed tube or system of tubes that operates in a low-pressure environment to reduce drag and increases efficiency to drastically reduce travel times [2, 3]. A fusion of advanced technologies that is used on high-speed railway (HSR), aviation, aerospace, and magnetic levitation applications is required for the successful implementation of the hyperloop and its safe integration into the current transport system [4].  
Since the first conception of the hyperloop, a significant amount of research and patent activity on several aspects of the hyperloop system components has been highlighted. Although there are other transport modes with similar components that can be used in hyperloop development, some hyperloop components differ substantively. For example, the hyperloop uses a propulsion system similar to the maglev trains but runs at higher speeds. Additionally, the pressure value that the pod supports is similar to conditions used in airplanes. Description of the hyperloop system components is provided in severalstudies [5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22]. Hyperloop studies focus on specific performance topics, such as aerodynamics [15; 18; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 44; 43], safety [8; 9; 16; 19; 20; 44; 45], and energy [7; 9; 14; 16; 17; 18; 23; 28; 39; 44; 46; 47; 48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58], while others focus on different hyperloop technologies, such as in the field of pneumatic tube and tunnel systems [18; 20; 23; 24; 28; 31; 42; 44; 53; 59; 60; 61]. The system functionality of certain technologies at a sub-scale level and low speeds has been proven; however, the compatibility of the various systems in subsonic speed ranges and at a real scale has yet to be verified [5; 11; 16; 20; 44].  
This fusion of technologies has engaged multiple public (e.g., MIT, UPV, EPFL, ETH, TU Delft, TU Munich, etc.) and private (e.g., Hardt, Hyperloop Transportation Technologies, Virgin Hyperloop, Zeleros, Nevomo, Swisspod Technologies, Transpod, etc.) stakeholders in the research and development of the hyperloop system in North America, Asia, and Europe. [PERSON] and [PERSON] [45] reviewed hyperloop scientific literature and patents, while the Hyperloop Standards Desk Review [3] provided a list of US stakeholders engaged in hyperloop R&D. Nonetheless, a list of EU stakeholders working on the hyperloop system and research directions per hyperloop component is not provided in the literature.  
Compared to those reviews, our study adds value by reviewing the most relevant literature to (1) describe the current state of progress for hyperloop system components and clusters information, (2) identify and present EU stakeholders per country engaged in hyperloop R&D, and (3) provide directions for future research per hyperloop component.  
In the remainder of this paper, Section 2 presents the methods used to identify literature for our review. The results in Section 3 include metrics and key features of reviewed publications, clustered information, identified EU stakeholders engaged in hyperloop activities, and a comprehensive analysis of the current state of progress for hyperloop components. We conclude the paper by providing directions for future research per hyperloop system component in Section 4.