long and seat both first and second class. There are 16 first class seats and 48 second class seats. They can seat 64 people, all on the upper deck, slightly lower than in the other coaches. There are no lower deck seats, as this is where all the electrical equipment is kept. Units with an mDDM are not in service as DD-ARs anymore, as they have been refurbished into DDZs. They are numbered from 390 7701 to 390 7750. Formations A multiple unit set made up of Bvs + ABv + Bv + mDDM can seat 448. This formation has a set number of 78xx and the last two digits are the same as the last two on the Bvs of the set. A push-pull train set made up of Bvs + ABv + Bv + Bv + 1700 locomotive can seat 588. This formation has a set number of 74xx and the last two digits are the same as the last two on the Bvs of the set. Modernisation from DD-AR to DDZ (NID) Nieuwe Intercity Dubbeldekker(NID) In 2009 NedTrain started to modernise 240, including the 50 mDDM coaches, out of 308 coaches of the DD-AR rolling stock. The other 68 coaches were intended to be taken out of service and sold or scrapped. The modernisation transformed the coaches to modern Intercity trains. The new name of the DD-AR is NID, which stands for Nieuwe Intercity Dubbeldekker ("New Intercity Double decker") and ride under the new DDZ (DubbelDekkerZonering) code. The upper decks will be quiet, meant for working purposes whereas the lower decks will be for fun and enjoyment. The 240 modernised coaches will form 30 EMUs consisting of ABvs + Bv + ABv + mBs (mBs = mDDM) and 20 EMUs consisting of ABvs + Bv + ABv + Bv + ABv + mBs; so a total of 50 EMUs will be formed. The first new EMU came into service in 2012, the last EMU in 2014. After the modernisation of the DD-ARs, the oldest 1700 series locomotives (from 1701 to 1729) are no longer used, since all new NID trains have a mDDM powercar. The trains went temporarily out of service on December 3, 2020 due to unexplainable shaking and noise at speeds from about 100 km/h. The cause of the shaking and noise was discovered to be worn wheels from the train's braking system; specifically, the