What is how many swing bridges are in the united states?

As an AI language model, I do not have access to real-time information and statistics. However, I can tell you that there are many swing bridges in the United States, particularly in areas with navigable waterways such as rivers and canals. Some notable swing bridges include the Blynman Canal Swing Bridge in Massachusetts, the Bridge of Lions in Florida, and the Bourne Bridge in Massachusetts, among others. The exact number of swing bridges in the United States is difficult to determine, as it is constantly changing due to construction, renovation, and demolition of existing bridges.