Roads & Bridges » The pace of improving the nation’s inventory of structurally deficient bridges slowed this past year. At current pace of repair or replacement, it would take 37 years to remedy all of them, said Dr. Alison Primo Black, chief economist for ARTBA. According to an analysis of the U.S. DOT’s just released 2017 National Bridge Inventory database, 54,259 of the nation’s bridges are rated structurally deficient.