Roughness and IRI
Pavement roughness is used around the world as a key performance measure for pavement life, user cost and user experience.
Pavement roughness is evaluated by measuring the accumulated difference in the height of a road surface (the longitudinal profile), independent of chassis response, over a prescribed road length. Roughness statistics are reported around the world using the International Roughness Index (IRI).
While traditional methods of IRI measurement rely on spot laser technology, and are limited to a single point in each wheelpath, the Pavemetrics® Laser Crack Measurement System (LCMS®-2) utilizes 3D line lasers capable of measuring 4,000 points across the entire lane width.
Key features of the LCMS roughness measurement methodology:
- Measurements are Class 1 precision and bias according to the ASTM E950 standard
- Has been independently certified at NCAT
- Longitudinal profile can be sampled every 1mm of travel (LCMS-2)
- Inspection speeds between 15 and 100km/h are supported
- Measurements are made independent of the vehicle chassis response using Inertial Measurement Units (IMU)
- IRI is calculated according to ASTM E1926
- Both IRI and HRI (half-car simulation) can be reported as frequently as every meter of travel
- Raw profile can be reported using the PPF and ERD formats for direct import into ProVal
Key advantages of the LCMS roughness measurement methodology compared to traditional methods:
- No need for a separate sensor system
- Full lane width profiling using 4,000 points versus just 1 point per wheelpath
- Tire-bridging algorithm to optimize roughness on tined and grooved surfaces
- Automated lane-tracking to correct for driver wander (improved repeatability and relevance of measurements)
- Automated filtering for potholes and other localized roughness features which can skew roughness values
- Advanced waveband analysis using three band pass filters for short, medium and long wavelength distortion reporting
E950; Can collect longitudinal profile and compute IRI with the precision and bias of a Class 1 Profiler
The Australian 3D Roughness Experience
Authors: Richard Wix and Simon Barlow (ARRB Group)
Advantages of Laser Scanning for 3D Road Profiling