The platform level is dominated by a 430-metre-long steel and glass roof construction, which, in terms of its load-bearing behaviour, is a true barrel shell. A high degree of transparency was achieved by resolving the structure into a network of steel linear members braced by diagonal cables. The roof is covered largely with flat panes of glass. At the crests of the arches are strips of ribbed metal sheeting raised above the roof line to facilitate ventilation. The main arched girders at 18 m centres span from platform to platform and accommodate the curving lines of the tracks by variations in their spans. The long faces at the sides are either closed by glazed façades or are terminated by curved cantilevered sections.