Sustainability 2023, 15, 725. https://doi.org/10.3390/su15010725 www.mdpi.com/journal/sustainability Article Economic Sustainability of High–Speed and High–Capacity Railways Filippo Giammaria Praticò and Rosario Fedele * DIIES Department, University Mediterranea of Reggio Calabria, 89124 Reggio Calabria, Italy * Correspondence: rosario.fedele@unirc.it Abstract: High–speed railways (HSRs or AV) and high–capacity railways (HCRs or AC, herein in the sense of open to freight trains) are crucial for the social and economic development of regions and nations. Their design, construction, and maintenance should comply with many requirements, including environment–, finance–, and policy–related ones. To this end, it is noted that the 2030 Agenda for Sustainable Development Goals (UN–SDGs, United Nations Member States, 2015) lists 17 targets, including decent work and economic growth (number 8), industry, innovation and cul- ture (n. 9), and take urgent action to combat climate change and its impacts (n. 13). Despite the above, when analysing costs, many uncertainties arise. In light of the foregoing, the main objectives of the study presented in this paper have been confined to the definition of a model for the estima- tion of HSR and HSR/HCR infrastructure cost. Theoretical considerations and data derived from Italian (both HSR and HSR/HCR), Spanish, and French HSR projects were used to set up and vali- date the proposed model. Results demonstrate that, under given conditions, it is possible to explain cost variability in terms of four main factors, namely high capacity (ACF), speed (SF), national (NF), and freight train factor (K), where this latter mainly refers to the need for longer tracks when freight trains are the main type of traffic. Keywords: high–speed and high–capacity railways; economic sustainability; infrastructure costs es- timation 1. Introduction The concept of sustainability refers to natural, social, and economic resources. As is well known, investments in transport infrastructure usually produce positive impacts on economic growth regardless of the type of transport [1,2]. Railway transport has a controversial influence on gross domestic product per capita (GDPC) because of the influence of many factors such as the emission of CO2 and other air pollutants [2]. Consequently, several studies have focused on the sustainability of rail- way projects. For instance [1], HSR projects promote socioeconomic development, even though it is needed to improve economic benefits and reduce negative environmental im- pacts (e.g., noise pollution can be reduced by adopting solutions such as noise barriers, tunnels, and overhead viaducts). Importantly, the sustainable development of HSR lines depends on three factors [1,3]: (1) the ability to adapt to the socioeconomic situation; (2) the ability to coordinate the development of several internal elements, such as infrastruc- tures, transport equipment, scheduling, service provision, and software–hardware inte- gration; (3) the ability to pursue green development (e.g., avoiding wasting land and non– renewable resources) and ecological harmony (e.g., reducing environmental pollution and accidents). According to [4], professionals may tend to adopt solutions that have low sustaina- bility and are far from the circular economy approach, despite the fact that they are able to identify and propose “sustainable ideas”. This behaviour can be explained in terms of Citation: Praticò, F.G.; Fedele, R. Economic Sustainability of High– Speed and High–Capacity Railways. Sustainability 2023, 15, 725. https:// doi.org/10.3390/su15010725 Academic Editor: Marco Guerrieri Received: 19 October 2022 Revised: 23 December 2022 Accepted: 25 December 2022 Published: 31 December 2022 Copyright: © 2022 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https://cre- ativecommons.org/licenses/by/4.0/).