The Lake Pontchartrain Causeway in Louisiana is the longest bridge in the United States. It's span of 23.83 miles (38.35 kilometers) makes it the longest continuous bridge over water in the world. That's a long way to travel over water! The causeway is actually two parallel bridges, allowing for double the traffic flow and providing some redundancy in case of maintenance or repairs. Supported by a whopping 9,500 concrete pilings, it can withstand the elements and the weight of heavy traffic. Why they had to build this bridge over a lake? The causeway serves as a vital link between New Orleans and the communities on the north shore of Lake Pontchartrain, making transportation and commerce much easier.