A bridge deck is like the floor of a bridge. Just like how we walk on a floor in a building, cars and trucks drive on the bridge deck to cross a river, a highway, or any other obstacle in their way. The bridge deck is usually made of concrete, steel or a combination of both. It's very strong and can hold a lot of weight, which is important because bridges need to be able to support heavy traffic. The deck is usually supported by beams or trusses that hold it up off the ground. So, a bridge deck is like the road on top of the bridge that vehicles use to get to the other side of the obstacle.