Measurements Parameters (Road Surface Profiler)
Longitudinal Profile, IRI and Ride Number
The longitudinal profile elevation measurements are obtained by using an accelerometer to monitor vertical vehicle body movement, and a laser sensor for measuring the displacement between the vehicle body and the pavement. Road profile elevation measurements are obtained by summing the vehicle body movement with the appropriate body-road displacement. Profile measurements in one or both wheel paths are possible. For the Mark III, if profile elevations are measured in both wheel paths simultaneously, it is also possible to measure profile elevations in the center of the lane, even if only a laser sensor is installed in that position. IRI is calculated in accordance with procedures and specifications outlined in World Bank Technical Paper Number 46 “Guidelines for Conducting and Calibrating Road Roughness Measurements”. Ride Number is calculated using methods outlined in “Measuring & Analyzing Road Profiles, National Highway Institute Short Course Manual, University of Michigan, Transportation Research Institute, October 1997”.
Rutting (Mark III only)
With a minimum of five laser sensors, a very simple lane “cross profile” and a simple, separate rut value for each wheel path can be calculated. By adding another two, four, six or more lasers (up to a total of 21), the transverse profile can be defined in greater detail, hence the rutting can be determined more accurately.
Texture
Any or both wheel path laser sensors can be of a texture-capable type employing smaller spot size and higher sampling frequency. For the Mark III the centerline laser sensor can also be texture-capable. The macrotexture statistics reported are in accordance with the established standard ‘Mean Profile Depth’ (MPD) and Root Mean Square (RMS). Both statistics are computed continuously and can be reported as close as every 100 mm (4 inches). Mean Profile Depth is measured according to ASTM E1845-01 “Standard Practice for Calculating Pavement Macrotexture Mean Profile Depth”.
The profiler can also calculate the RMS (Root Mean Square) of the profile trace, which provides additional useful information regarding pavement texture (for further information, see “High-Speed Texture Measurement Of Pavements”, Kevin K. McGhee, P.E., Gerardo W. Flintsch, Ph.D., P.E., Virginia Polytechnic Institute & State University, Virginia Transportation Research Council, February 2003).
Crossfall, Grade, and Radius of Curvature (Mark III only)
By adding an Inertial Motion Sensor (IMS), collection of crossfall, grade, and highway curvature information is possible. The IMS is a microprocessor controlled, self-compensating, three-axis solid-state gyro unit. Crossfall is computed as the slope of a linear regression line through the laser elevation measurements, adjusted for roll information obtained by the gyro. Crossfall is displayed and stored in degrees.
Grade is the longitudinal slope of the lane under test. It is displayed and stored in degrees.
Radius of Curve (km or mile) and Curvature (deg/km or deg/mile) of the lane is determined in the horizontal plane. Turn rate (degrees per second) and the vehicle velocity are the basis for these computations.
Laser Elevations and Accelerations
Raw laser elevation data (height of each laser above the pavement surface) and raw vertical acceleration can be stored at user-specified intervals. Elevations determine the Cross-Profile and are useful for verifying rut measurements or providing data from which to calculate rut depths using alternative procedures.
Faulting
Faulting on jointed concrete pavements can be detected according to “Standard Practice for Estimating Faulting of Concrete Pavements AASHTO Designation: PP39-99”. The RSP field program provides ample flexibility for the user to specify and/or modify the definition of a fault.