The central train shed today serves as a terminal station with seven tracks running from the west. Originally, however, it housed only six platform tracks. Even before the Second World War another platform track was integrated into the train shed, the current platform 14. This change involved the abolition of two luggage platforms, leaving only the former luggage platform between platforms 6 and 9. The tracks of the central part of the station are approximately at street level, while all the through tracks run in a second level which is about 4.50 metres higher. The north and south halls house three through tracks (without platforms) that run in a southeasterly direction past the terminal hall. The eastern sections of platforms 1 and 2 are also referred to as platforms 1a and 2a. The north hall also houses an additional through track without platform. During the refurbishment works carried out since 2000, the platform height was adjusted to meet current standards. The east wing originally had a second terminal track, but only platform track 4 is still in use. In addition to structural changes, the system of operations has also changed. It was initially mainly operated with tracks arranged according to direction (that is with fast and slow lines in the same direction). The tracks are now largely arranged as discrete lines (for instance some tracks are dedicated to S-Bahn services). The following table gives an overview of the aspects of the platform and their original and current use (November 2009). The island platform added between the freight tracks south of the south hall in the 1930s has not existed since the reorganisation in the new millennium and therefore it is not shown in the table. Roof construction A special feature of the station is the renovated roof, which was designed by the British architect Sir Norman Foster. The previous panes of framed glass were replaced by 0.7 mm-thick glass fibre membranes which have been stretched between the arched halls. The membranes have double-sided Teflon coatings that are 0.1 mm-thick and are self-cleaning. It was the first time that a historic building had been treated with this new material. Designed for a service life of 50 years, the membrane can resist tensile forces of up to about 150 kN per metre. It can be walked over by trained personnel with a safety harness. The membrane is largely translucent during the daytime