Why Roadway Funding and Pavement Smoothness Should Be Considered Together

Smoother roads create major economic and environmental benefits, and those benefits increase as pavement smoothness improves. Achieving very low roughness levels across an entire state highway network may not be immediately practical with today's budgets. However, our research (link to report) using data from the Oregon roadway network managed by Oregon DOT shows that meaningful progress toward smoother roads can yield substantial returns. Moving the network toward smoother conditions could produce estimated savings of approximately $190 million per year from reduced vehicle fuel and energy use and tire wear alone, even after accounting for Oregon's projected electric vehicle growth. These results show that roadway funding decisions should not be made only by considering agency construction costs. They should also account for the costs and savings created for road users and for the environmental impacts of the pavement use phase.

The key parameter in this relationship is roadway roughness, commonly measured using the International Roughness Index, or IRI. Lower IRI values indicate smoother pavements, while higher values indicate rougher ones. Rougher surfaces increase vehicle suspension movement and rolling resistance, resulting in higher fuel consumption, higher tire wear, higher vehicle operating costs, and higher carbon emissions. Pavement roughness is not only a ride quality issue. It is also an economic and environmental issue.

Reduced paving funding creates costs somewhere else

When pavement preservation programs are underfunded, fewer roadway miles can be maintained at the right time. This results in declining pavement conditions, increased roughness, and the need for more expensive rehabilitation in the future. The cost of underfunding does not disappear. A significant portion transfers directly to road users through higher fuel consumption, increased tire wear, and increased travel discomfort.

Pavements are not like light bulbs. They cannot simply be used until they stop working and then easily replaced. Once pavement sections start to fail, the relationship between time and maintenance cost becomes very steep. A treatment that could have been simple and cost-effective at the right time can turn into a much more expensive rehabilitation or reconstruction need if delayed. The pavement use phase can be a major contributor to both life-cycle costs and greenhouse gas emissions. Vehicles use the roadway network every day for many years after construction, so even small changes in vehicle energy use caused by roughness become very significant at the network level.

The calculated savings are very significant

Our study quantified the impact of roadway roughness on road user costs and greenhouse gas emissions using data from the Oregon roadway network managed by ODOT. The results show that even moderate improvements in network-level smoothness can create substantial savings, and that the benefits increase as smoothness improves further.

Looking at the past 20 years of Oregon IRI data, the estimated annual savings from reduced excess fuel consumption and tire wear would have been approximately $45 million per year if the network had been maintained at an average IRI of 65 inches/mile. If the network had been maintained closer to an average IRI of 40 inches/mile, those savings would have increased to approximately $142 million per year, exceeding the approximate annual ODOT paving budget used in the study comparison.

The emission savings follow the same pattern. Maintaining the network at an average IRI of 65 inches/mile would have produced approximately 134,927 metric tons of CO2 savings per year, close to ODOT's full annual operational emissions. Maintaining the network closer to an average IRI of 40 inches/mile would have produced approximately 423,462 metric tons of CO2 savings per year, which is approximately 2.3 times ODOT's total annual operational emissions.

Future projections reinforce the same message. If the roadway network could be moved closer to an average IRI of 40 inches/mile over the next 10 years, the estimated savings would be approximately $190 million per year, even after accounting for Oregon’s projected EV growth, along with more than 542,000 metric tons of CO₂ savings per year. Although this is an ambitious long-term target, better paving technologies, improved mix designs and construction materials, better preservation timing, and expanded use of new tools and performance monitoring systems could make it more achievable. The results show that moving network-level roughness from approximately 65 inches/mile toward 40 inches/mile can create very large economic and environmental benefits, even if the 40 inches/mile target is not fully achieved.

Smoother roads also improve long-term pavement performance

The savings discussed above are based mainly on reduced excess fuel consumption and tire wear. However, smoother roads can also improve the long-term performance of the pavement structure itself. Rougher pavements generate additional dynamic impact forces as vehicles, especially heavy trucks, travel over the surface. These higher forces accelerate pavement damage, increase deterioration rates, and shorten pavement service life. Research has shown that a 25% reduction in roughness can increase pavement life by approximately 11 to 28 percent, while a 50% reduction can increase pavement life by approximately 18 to 55 percent, depending on pavement type and conditions. This means the savings calculated in this study likely underestimate the full benefit of smoother roads.

Funding is needed, but better engineering is also needed

Increasing roadway funding is critical because more frequent preservation and paving are needed to reduce network-level roughness. However, funding alone is not the complete solution. Continued improvements in balanced mix design, aggregate gradation selection, plant production consistency, paving practices, compaction, and quality assurance are also needed to construct smoother pavements and keep them smoother for longer. Oregon's current after-construction IRI target is 60 inches/mile, but the results of this study show that pushing below this target, when feasible, can create growing economic and environmental returns.

The goal should not only be to pave more. The goal should be to pave more, pave at the right time, and pave better.

Electric vehicles do not eliminate the importance of smooth roads

As Oregon's vehicle fleet becomes more electrified, smooth roads will continue to be important. Electric vehicles reduce tailpipe emissions, but they still consume energy, still experience tire wear, and their batteries and electricity production carry their own environmental impacts. Rougher roads can increase EV energy consumption, similar to their effect on fuel consumption in conventional vehicles. Roadway smoothness should be considered a long-term energy efficiency strategy, not only a fuel-saving strategy. As electric vehicle use increases, smoother pavements can improve energy efficiency across the entire fleet and help reduce future demand on the electric grid.

Conclusion

Oregon’s data provides a clear case that smoother roads create measurable, large-scale economic and environmental benefits, and that these benefits increase with every meaningful improvement in network-level smoothness. Achieving very low IRI values is a long-term goal, but advances in paving technologies, improved materials and mix designs, better preservation timing, and stronger construction practices are making this goal increasingly attainable.

Adequate roadway funding, combined with better materials and construction practices, can reduce costs for road users, lower emissions, and improve the long-term performance of the roadway network. Roadway funding decisions should reflect this full picture.