The FHWA is working on a plan called Bridges for the 21st Century to maintain and build bridges that last longer. They are looking at ways to preserve existing bridges more efficiently. There are over 480,000 bridges in the US, with an average age of 42 years. Bridge failures are often caused by de-icing salts and being near marine environments. The FHWA wants to monitor 1,000-2,000 bridges over 10-20 years to understand how different types of bridges perform over time.