An hourly regional train service connects Liberec (Czechia) with Zittau (Germany), but this train is not as efficient as it could be as it can run at only 40km/h on a 2.7km section of dilapidated track that crosses Polish territory at Porajów, just south of Zittau. The rest of the service is on tracks rated at 80-100km/h, and the slow section through Poland prevents good onward connections in Zittau.
What needs to be done: Czechia and Germany need to find a financial arrangement with Poland to repair the track, and increase speeds to 100km/h. The land is flat, so this would not be technically difficult or especially costly. Two level crossings would need upgrading
European Commission Analysis
In 2018 the European Commission published its “Comprehensive analysis of the existing cross-border rail transport connections and missing links on the internal EU borders”. The main report (74 pages, PDF) summarises the issues, and Annex 3 of the report (384 pages, PDF) analysed every single border.
For the sake of simplicity, I have made a PDF just of the relevant pages of Annex 3 that cover Liberec-Porajów-Zittau – you can find that PDF here.
Photos from this location