Nepal-China cross border railway, during the second Belt and Road Forum (BRF), was listed as a part of trans-himalayan connectivity network. The train project was discussed in two meetings held in Beijing and Kathmandu in 2019. It involves laying 72 kilometers of rail tracks from Kerung in southern Tibet to Kathmandu, entering the country in Rasuwa district and eventually linking to Lumbini, a town close to Indian border. China’s pre-feasibility for railway project, conducted in 2018, mentioned various challenges to the project including environmental and engineering concerns. Though the budget for project has not been set so far, study estimated it will cost USD 5.5 billion. It is reported that railway will take long time to materialize owing to geological, technical and engineering concerns. Some locals have expressed serious concerns regarding biodiversity and environmental issues. Locals have realized that the prices of land along Kathmandu-Rasuwa Gadhi highway have soared after railway project was announced. Experts anticipated that train project would be costly and challenging (Technically and financially) for Nepal. China, since 2019, has delayed its commitment to finance detailed project report which is yet to be delayed for another four years.
Source
https://mofa.gov.np/wp-content/uploads/2020/12/Report-on-Nepals-Foreign-Affairs_MOFA_2019-2020.pdf
https://kathmandupost.com/national/2018/08/16/rail-project-complicated-and-arduous