With the exception of the Hammersmith Flyover the superstructures of these bridges generally conform to three main types: (a) single cell box girder, (b) pair of single cell box girders connected by the deck slab, and (c) multicell box girder. These types are sketched in Fig. 2. The prestressing systems used depend partly on the type of cross section, the structural system,and the method of construction, but vary greatly from bridge to bridge. Several of the bridges included in Table 1 are described in detail in the following sections.