Which statement best describes the relationship between pavement International Roughness Index (IRI) and smoothness?

Which statement best describes the relationship between pavement International Roughness Index (IRI) and smoothness?

• A. Higher IRI indicates smoother pavement
• B. Higher IRI indicates rougher pavement
• C. IRI is unrelated to roughness
• D. IRI measures only asphalt wear

Answer: (B)

The main concept here is that the International Roughness Index (IRI) is a measure of pavement ride quality that reflects how rough the surface feels to a vehicle. Lower IRI values indicate a smoother ride, while higher values mean more bumps and vibrations—so a higher IRI corresponds to rougher pavement. This happens because IRI is derived from the road profile and how it translates into suspension and wheel movement; larger deviations from a straight profile produce greater jolts, leading to a higher IRI. The other statements don’t fit because IRI is directly tied to roughness and ride quality, not to smoother conditions, unrelated to roughness, or limited to asphalt wear.

The main concept here is that the International Roughness Index (IRI) is a measure of pavement ride quality that reflects how rough the surface feels to a vehicle. Lower IRI values indicate a smoother ride, while higher values mean more bumps and vibrations—so a higher IRI corresponds to rougher pavement. This happens because IRI is derived from the road profile and how it translates into suspension and wheel movement; larger deviations from a straight profile produce greater jolts, leading to a higher IRI. The other statements don’t fit because IRI is directly tied to roughness and ride quality, not to smoother conditions, unrelated to roughness, or limited to asphalt wear.