feasibility study published already in 2016 identifies research topics related to Hyperloop technologies [7].  
After the white paper and the initial hype, several companies in the US brought together engineers and venture capital money to perform research and development and make Hyperloop a reality [8]. Later on, the same companies expanded to Europe, and other Europe-based companies engaged in similar activities [9], including the planning and development of Hyperloop test sites.  
Furthermore, recent developments regarding the need for standardization in Europe and the US highlight the interest in the regulation of Hyperloop. In Europe, the \"Sustainable and Smart Mobility Strategy\" was presented in December 2020 by the European Commission and the accompanying action plan of initiatives will guide its work for the next four years. Among the objectives of this plan is to \"assess the need for regulatory actions to ensure safety and security of new technologies and concepts such as Hyperloop\" [10]. Before that, a new Joint Technical Committee (TC), CEN/CLC/JTC 20, was launched by the European Committee for Standardization (CEN) and the European Committee for Electrotechnical Standardization (CENELEC) to address the need for the standardization of Hyperloop systems [11]. A year before, in 2019, the U.S. Department of Transportation (DOT) created the Non-Traditional and Emerging Transportation Technology (NETT) Council, an internal body with the objective of identifying and resolving gaps, either legal or regulatory, that may obstruct the deployment of Hyperloop, among other new technologies [12]. In January 2021, the NETT Council presented the \"Hyperloop Standards Desk Review\" with the scope of assessing the status of Hyperloop standardization activities, developing a foundation for future Hyperloop standardization efforts, and consequently, paving the way towards the development of a preliminary framework of Hyperloop system components and associated regulations and voluntary technical standards [13].  
The dynamics of the technology and the progress made toward future Hyperloop deployment in Europe is highlighted by a recent mapping of activities in the industry and European institutions [14]. Nevertheless, to test the safety, efficiency and reliability of Hyperloop in the field, beyond research and development (R&D), a long enough, full-scale prototype track is necessary.  
Beyond the US and Europe, in China and Korea, as patent activity shows, there is substantial R&D from CRRC Yangtze Co., the Korea Railroad Research Institute (KRRI) and the Korea Institute of Construction Technology (KICT) [14; 15].  
Considering the above, this study examines the status of Hyperloop scientific developments, identifying issues and challenges. It is based on initial considerations developed in [14]. Compared to that previous study, a systematic review was performed, and the fields of research were explicitly identified. Consequently, a taxonomy of scientific research issues was developed by analyzing all Hyperloop research in the literature, using the methodology developed by the European Commission's Transport Research and Innovation Monitoring and Information System (TRIMIS) [16]. Accordingly, the literature was organized in relevant clusters and for each cluster combination, the issues were identified as lower-level items in the taxonomy.  
The findings could be of help to transportation academics and professionals who are interested in developments in the field, and form the basis for policy decisions for the future implementation of Hyperloop.  
The paper consists of the following parts: after the introduction, the next section discusses the materials and methods used in this study, drawing from the Scopus database and a physical system decomposed into several clusters. Section 3 provides the results from the analyses grouped under the different clusters. Section 4 provides an initial taxonomy based on the performed analysis and a brief discussion. Section 5 provides the conclusions.