andyfabian - it is two way as haynewp says....Two way slabs are designed as one way strips made up of column and middle strips per the equivalent frame method of ACI 318. This design is performed in the two orthogonal directions and combined to form crossing column and middle strips of reinforcing.
If you've ever seen a slab like this reinforced in the field, from a bird's eye perspective it looks like a plaid-type layout with dense steel at columns, moderate steel in strips along column lines, and lighter steel in the mid-bay areas.