The three-car dmus were ordered in March 2009 and are a development of the class 3000, 23 of which were supplied by CAF to Translink between 2002 and 2004. The class 4000 is five tonnes lighter than its predecessor and features a driver assist system for more efficient acceleration and braking, fuel-efficient transmission, and reduced exhaust gas emissions to comply with EU Stage IIIA standards. Each train accommodates 212 passengers, 12 more than the class 3000, and there are new multi-purpose areas to accommodate pushchairs and bicycles. Two more trains will arrive in the next few weeks and three sets will undergo simultaneous testing this summer. The first trains will enter service on the Belfast - Larne line and all 20 will be deployed by the end of next year. In preparation for the introduction of the Class 4000s a programme of infrastructure improvements is underway including platform extensions at 19 stations and a new maintenance depot at Adelaide in Belfast. Longer-term enhancements include an upgrade of the Coleraine - Londonderry line, which is scheduled to take place in 2014-15.