Stock (A and C Stock lacked DMIs). The DMIs show destination and line, and can display other messages such as safety notices. There are also DMIs on the exterior, with text alternating between destination and line, and on S8 Stock the stopping pattern (fast, semi-fast or all stations). The S8 Stock is the first on the Metropolitan line with dot-matrix indicators and automated voice announcements. The air-conditioning system, the first on London Underground trains, is supplied by Mitsubishi and has two circuits so that if one fails there is still 50% capacity. Open gangways from car to car (similar to London Overground's Class 378) allow passengers to move from crowded cars to ones with more room, provide extra room for standing, and create a sense of security. CCTV enables the driver to see into every car, while track-to-train video links give the driver a view of the train exterior before leaving a station. There is a fold-out set of steps in each driver's cab to allow fast evacuation in an emergency. The S stock has cantilevered seating for easy cleaning and accessible storage of bags. The seating configurations are different between the two models of trains: the S7 Stock, used on inner city lines with higher passenger traffic, has longitudinal seating throughout, while the S8 Stock, used for the longer journeys from the outer suburbs, has a mix of transverse and longitudinal seating, with four wheelchair spaces per train. S7 Stock trains are long, while the S8 trains measure . To prevent accidental pressing of emergency alarms, there are flaps over the alarm buttons next to wheelchair spaces. Although S Stock trains can operate on all four sub-surface lines, S8 trains are used on the Metropolitan line and S7 trains are used on the other three lines. Selective door operation is used at certain stations that are shorter than the train. S7 Stock has seven cars per train, while S8 Stock has eight. Design icon As part of the Transported by Design programme of activities, on 15 October 2015, after two months of public voting, the walk-through S Stock train was elected by Londoners as one of the 10 favourite transport design icons. Entry into service Following the implementation of the London Underground Public Private Partnership (PPP) in 2003, the Metronet consortium became responsible for the infrastructure on the District, Circle, Hammersmith & City and Metropolitan lines. As part of