International Roughness Index, the standard measure of pavement smoothness, calculated from a longitudinal profile collected by an inertial profiler with lasers and accelerometers. The profile is run through a quarter-car model that estimates how much a vehicle suspension would move, expressed in inches per mile or meters per kilometer. Smooth new asphalt often measures well under 60 inches per mile while badly worn roads run past 170, and many contracts pay incentives or deductions on IRI.
IRI on the eastbound came in at 48, that's full bonus, but the bridge approaches dragged the westbound up to 72.
Also heard as
- International Roughness Index
Related terms
Ski
Crew name for the long averaging beam on a paver that gives the grade sensor a smoothed reference.
Pay factor
A multiplier applied to the contract price for a lot of asphalt based on its test results.
Paver
The self-propelled machine that receives hot mix, spreads it to width and lays it as a smooth, partly compacted mat.