https://www.politico.eu/article/germany-9-euro-ticket-train-public-transport/?utm_source=POLITICO.EU&utm_campaign=41557aa1fc-EMAIL_CAMPAIGN_2022_10_14_11_29&utm_medium=email&utm_term=0_10959edeb5-41557aa1fc-190380769
https://www.ips-journal.eu/index.php?id=326&L=0&tx_news_pi1%5Bnews%5D=3904&tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&utm_source=newsletter&utm_medium=email&utm_campaign=en_728_20191129&cHash=5d8677e040088390be92d9eb2a20fb32
https://images.transparencycdn.org/images/Report_CPI2022_English.pdf