*Article* **Urban Air Mobility: Systematic Review of Scientific Publications and Regulations for Vertiport Design and Operations**

**Karolin Schweiger 1,\* and Lukas Preis <sup>2</sup>**


**Abstract:** Novel electric aircraft designs coupled with intense efforts from academia, government and industry led to a paradigm shift in urban transportation by introducing UAM. While UAM promises to introduce a new mode of transport, it depends on ground infrastructure to operate safely and efficiently in a highly constrained urban environment. Due to its novelty, the research of UAM ground infrastructure is widely scattered. Therefore, this paper selects, categorizes and summarizes existing literature in a systematic fashion and strives to support the harmonization process of contributions made by industry, research and regulatory authorities. Through a document term matrix approach, we identified 49 *Scopus*-listed scientific publications (2016–2021) addressing the topic of UAM ground infrastructure with respect to *airspace operation* followed by *design*, *location and network*, *throughput and capacity*, *ground operations*, *cost*, *safety*, *regulation*, *weather* and lastly *noise* and *security*. Last listed topics from *cost* onwards appear to be substantially under-represented, but will be influencing current developments and challenges. This manuscript further presents regulatory considerations (Europe, U.S., international) and introduces additional noteworthy scientific publications and industry contributions. Initial uncertainties in naming UAM ground infrastructure seem to be overcome; *vertiport* is now being predominantly used when speaking about vertical take-off and landing UAM operations.

**Keywords:** urban air mobility; UAM; eVTOL; vertiport; literature review

## **1. Introduction**

*"To take off, flying vehicles first need places to land"* [1]

The interest in suitable VTOL ground infrastructure is rising due to the growing amount of small UAS applications and the thriving topic of UAM introducing a new mode of passenger transport and on-demand deliveries inside urban areas. UAM is striving for revolutionizing the status quo of ground transportation, aircraft design, ATM processes and the principles of multi-modality. Furthermore, UAM seeks to connect residential areas and airports to city centres, to attract as many residents as possible by promising immense time savings under affordable conditions. UAM is setting the scene for new approaches, new technologies and new potential markets. However, UAM is describing a new mode of aerial transportation which will be implemented in very challenging urban environment in which VTOL capabilities and early considerations of infrastructure design specifications are expected to be crucial. This is supported by EASA "Study on societal acceptance of Urban Air Mobility in Europe" which concluded with infrastructure being the biggest challenge for UAM [2].

These days, the topic of UAM is thriving, the number of published contributions is large, but those who focus specifically on UAM ground infrastructure are widely scattered

**Citation:** Schweiger, K.; Preis, L. Urban Air Mobility: Systematic Review of Scientific Publications and Regulations for Vertiport Design and Operations. *Drones* **2022**, *6*, 179. https://doi.org/10.3390/drones 6070179

Academic Editors: Ivana Semanjski, Antonio Pratelli, Massimiliano Pieraccini, Silvio Semanjski, Massimiliano Petri and Sidharta Gautama

Received: 19 June 2022 Accepted: 12 July 2022 Published: 19 July 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

and are addressing different business cases, time horizons and technological readiness. This manuscript provides a detailed and systematic review of 49 *Scopus*-listed, scientific publications about ground infrastructure in the context of UAM and published between the years 2016 and 2021 (including). The publications were selected through a text mining approach: if the abstract of a publication contained both "urban air mobility" and at least one keyword related to ground infrastructure (see the list of keywords in Section 1.1) it was included in the selection. The various text mining techniques used in the analysis are explained in Sections 1.2 and 1.3. These encompass database overlap analysis, document term matrix and document classification. All scripts were written by the authors using the following *Python 3.8* packages: *pandas*, *nltk*, *stop\_words* and *statistics*. A comprehensive introduction into the text mining approaches used in this review can be found in [3].

The review predominantly focuses on VTOL operations and subsequently calls UAM ground infrastructure: *vertiports*. Furthermore, additional noteworthy contributions made by research, regulatory authorities and industry are presented. This review complements already existing UAM review publications of Garrow et al. [4] and Straubinger et al. [5] and contributes thereto by focusing explicitly on ongoing research, regulatory and industrial contributions as well as intermediate achievements in the field of UAM VTOL ground infrastructure. We are aware that the term "urban air mobility" indicates a limited view compared to "advanced air mobility" (AAM) as proposed by NASA [6]. Yet NASA continues to use the term UAM as a subset of AAM, as do comprehensive reviews of the field [4,5]. For this reason we will use the term UAM, but we do not intend to exclude other applications of AAM, such as regional or rural air mobility.

Throughout the review, eleven research topics were identified: *airspace operation*, *design*, *location and network*, *throughput and capacity*, *ground operations*, *cost*, *safety*, *regulation*, *weather*, *noise* and *security* (sequence: descending prominence), which shaped the following structure of the manuscript. Section 1 provides an overview and a systematic trend analysis (text mining) of already used UAM ground infrastructure terminology and classifications. Section 2 elaborates a summary of current heliport design guidelines and introduces first drafts and prototypes of vertiport design specifications focusing mainly on European and American contributions. The subsequent Sections 3–5 summarize and discuss the contributions of 49 publications based on the trend analysis introduced in Section 1. Additional noteworthy scientific, regulatory and industry contributions are discussed. Section 3 examines the development of vertiport networks considering different operating environments and groups of customer. Section 4 summarizes vertiport design proposals, analyzes different approaches of developing vertiport airside air and ground operations and collects initial investment estimations for specific vertiport designs. Section 5 concludes the review by providing initial evaluations of weather impacting UAM and vertiport operations. Finally, Section 6 conducts a critical evaluation of all sighted contributions and highlights pending and under-represented research questions.
