Influence of the Covid-19 Pandemic on the Development of the Railway Transport in Bulgaria. Научни трудове на УНСС, [S. l.], v. 5, p. 281–293, 2023. DOI: 10.37075/RP.2022.5.15. Disponível em: https://ojs.e-dnrs.org/rpunwe/article/view/285. Acesso em: 6 dec. 2025.