
http://www.aviationlaw.eu/wp/wp-content/uploads/2013/09/Freedoms-of-the-Air-Explained.pdf

https://wiiw.ac.at/the-emissions-reduction-potential-for-freight-transport-on-a-high-speed-rail-line-along-the-european-silk-road-dlp-6635.pdf

https://ecipe.org/wp-content/uploads/2019/03/ECI_19_OccasionalPaper_Competition_01_2019-1.pdf