Once the girders have been erected, diaphragm supports, made of steel-reinforced concrete, are built between the girders to lend support to the bridge deck. The final step in bridge building is construction of the deck. The deck has two structures, an interior structure and an exterior structure. The interior deck forms, which may be solid concrete panels or wood forms, are placed on top of the superstructure. The concrete deck is about 10 inches thick.
Vehicles drive on the deck.
There will be more than 50 bridges in the Big I project. What might look like a single bridge may actually be two or more bridges joined together.