Is there a doctor in the house to check on this bridge? A bridge is like a living organism. It requires frequent health check-ups and maintenance, and its lifespan is 50 years on the average. With limited resources and an aging bridge population, bridge owners need reliable information on bridge health in order to manage their bridge inventory efficiently and economically. Although the tragic bridge collapse in Minneapolis in the summer of 2007 was not attributed to poor maintenance, everyone was reminded of how crucial understanding bridge health and performance is to the safety of the motoring public.