The purpose of bridges is not only to allow movement on the surface being constructed but also to permit motion below. This bridge crosses a major waterway (the Delaware River is the longest undammed river (282 miles) east of the Mississippi). This is a "working river" with commercial, international maritime traffic headed to piers north of the bridge and cargo to the Atlantic Ocean and the rest of the world. The bridge allows all but the largest boats to pass under and the limiting factor for shipping is often the depth of the river rather than the height of the bridge.
Here are some photos of ships passing below the bridge.