Exploring the relationship between the International Roughness Index (IRI) and the ISO 8608 roughness coefficient (G_d(n₀))

ABSTRACT

Globally, diverse agencies employ varied metrics to gauge road roughness, complicating the exchange of information for pavement maintenance. This study addresses this challenge by establishing a theoretical connection between the International Roughness Index (IRI) and the ISO 8608 Power Spectral Density (PSD)-based roughness coefficient, namely G_d(n₀). Based on random vibration theory, this paper first deduces a closed-form explicit solution for IRI related to G_d(n₀), solidifying a theoretical link. Next, the variability and convergence of the proposed solution are examined through Monte Carlo simulations using a quarter-car vehicle model with the Golden Car parameters. Then, we compare computed results from this study with those existing solutions from past studies, verifying that the proposed solution captures the curve trend well and agrees with the average value of existing solutions based on field measurement data. Finally, this paper proposes the IRI values corresponding to various ISO road class thresholds and a new G_d(n₀) scale for ride quality assessment of highways.

KEYWORDS:

• Road roughness
• International Roughness Index (IRI)
• ISO 8608 roughness coefficient (G_d(n₀))
• Power Spectral Density (PSD)
• quarter-car vehicle model
• ride quality

Disclosure statement

No potential conflict of interest was reported by the author(s).