The function of the street level has yet to be decided. The design separates street level from the upper levels so that the whole will be functional no matter how the street level is used. The uppermost level is covered by a flowing shape made up of a series of connected surfaces, some of which fold down to enclose part of the concourse level. The shape varies along the longitudinal axis, with no two points having the same section. This type of exterior tends to be easily soiled by trails left when rainwater flows over it. To reduce this, rain gutters were inserted at several points as horizontal slits in the surface. This gives an effect like slits cut with a knife into a fluid surface, similar to a garment made by inserting slashes into a single piece of cloth.