NS was alerted to the vibrations by staff, but an initial study was unable to determine the source of the issue. A second investigation is now underway.
The fleet will be replaced by rolling stock which is currently out of service due to the coronavirus pandemic.
DDZ comprises a BoBoBo powered vehicle, with seating on the top level, and either three or five double-deck trailer coaches with NS operating 30 four-car and 20 six-car sets.
NS launched a market consultation in April ahead of a tender to replace the DDZ fleet from 2027.
