The U.S. National Highway System (NHS) – the federally managed bridge and road network that moves American people and goods – has suffered from decades of insufficient maintenance and heavy use. Lack of funds, increasing traffic loads, and environmental exposure have encouraged rapid bridge deterioration in an already aging system. In 2016, nearly 40% of the nation’s bridges were over 50 years old and 9.1% were rated “structurally deficient.” To properly prioritize maintenance, repairs, and reconstruction, the Federal Highway Administration (FHWA) has implemented the National Highway Performance Plan (NHPP), which requires states to design and implement management strategies for their NHS assets.

To fulfill Montana’s NHPP requirements, two WTI employees, Senior Research Engineer Damon Fick and Researcher Matt Bell, have developed a bridge assessment program for the Montana Department of Transportation (MDT) using three decades of inspection and deterioration data. By performing a time-based statistical analysis on these data Bell and Fick were able to create graphical deterioration projections – or Deterioration Curves – for bridges across the state. These were then adjusted to better reflect the deterioration observed in MDT’s real-world observations. “These bridge deterioration curves guide maintenance planning and decision-making at both the project and network level,” noted Bell. “By reflecting what we see in the real world, MDT can use the curves to appropriately allocate money for future work and make sure maintenance is happening at the right time.

While the deterioration curves indicate the general deterioration rate of bridges across Montana, Bell and Fick will identify specific deterioration variables (deicers, precipitation, traffic volume, etc.) in their next MDT project. “Faster or slower deterioration rates in different Montana districts may be related to maintenance practices, as much as, or in combination with, environmental conditions,” said Bell. “For example, bridges that permit heavy truck loads may experience faster deterioration. If we understand the specific impact, MDT can improve truck permitting and preemptively identify maintenance activities and building specifications. Continually improving the accuracy of the deterioration curves will support the decision-making process for our colleagues at MDT.”