The modernisation of the U4 underground line ("NEU4") is the largest round of modernisation work to be performed in the history of the Vienna underground system.
The City of Vienna and Wiener Linien are investing EUR 335 million in the NEU4 project to improve the U4 underground line. This modernisation work includes the replacement of signal boxes and the renovation of tracks, track foundations, stations and tunnel ceilings. Additional track connections will also make it possible to change tracks in the event of disruptions, helping to improve the reliability of the U4’s operations.
Work began in spring 2014 and will continue until 2024; in the final phase after 2019, however, this work will have a negligible impact on U4 operations.