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The road-monitoring community is considering alternatives to the International Roughness Index (IRI) that are based on the Golden-Car model, but perform the simulation at a speed other than standard value of 80 km/h. Many state and federal highway agencies apply pay adjustments to new road and road resurfacing contracts based on the IRI, but expect significantly higher prevailing travel speeds on very smooth limited-access roads. Inertial profilers also continue to propagate as a tool for monitoring pavement conditions on lower-speed roads, where the posted speed limit or the prevailing traffic speed may be much lower than 80 km/h. The broad application of the IRI to higher and lower-speed roads has created interest by practitioners in the issue of Golden-Car model simulation speed. Changing the simulated forward speed causes predictable changes in the frequency response of the Golden-Car model: the temporal frequency response changes very little, but the spatial frequency response shifts in proportion to speed. However, the quantitative effect on the resulting index values and their relationship to other relevant responses, such as tire load variations and passenger acceleration, are less obvious. This paper explores the potential consequences of changes to the Golden-Car model simulation speed, including changes to the output roughness values and meaning of the roughness scale and roughness threshold values. Most of the discussion relies on numerical and theoretical analysis, with some sample measurements provided for elucidation.
road roughness, International Roughness Index, road profile, vehicle simulation
Karamihas, Steven M.
Univ. of Michigan, Dept. of Mechanical Engineering, Ann Arbor, MI