From quality control of new pavements, to validation of high speed equipment, to calibration/control site setup, ICC has you covered.
Roads that are smooth when first paved last longer, stay smooth longer, and are safer. All states have smoothness requirements in place for new pavements, and more states are implementing incentive/disincentive programs for paving contractors based on the achievement of specific smoothness levels.
The most common smoothness indices are the International Roughness Index (IRI) and the Profilograph Index (PrI). Both are readily measured by ICC’s IrisPRO system, which can be mounted on a truck (i.e. a high speed profiler), or on a side-by-side or similar utility vehicle (i.e. a lightweight profiler). ICC’s SurPRO walking profiler can also measure an extremely accurate profile in cases where that is required.
ICC provides inertial profiling and smoothness measurement as a turnkey service.
Departments of Transportation (DOTs) must establish calibration and control sites to validate the equipment being used to collect road condition data. The control procedure must be documented in their Data Quality Management Plan (DQMP).
Establish control sites requires the collection of reference data on those sites. The reference data is collected using highly-accurate, certified equipment. The reference data becomes the set of “known values” to which data collected by the high speed equipment is compared.
U.S. states are required by the federal government to have a Data Quality Management Plan (DQMP) in place that ensures proper equipment calibration and verification procedures are maintained for the duration of network-level testing.
Control Site Selection
Control sites should be selected to be representative of the pavement types and conditions throughout the network. A minimum of 5 sites should be selected, including at least 3 asphalt (ASP) sites ranging from new to old, and at least 2 jointed concrete (JCP) sites ranging from new to old. If continuously-reinforced concrete pavement (CRCP) is used in the network, then at least one site with this pavement type should also be selected.
The ride quality on the set of selected ASP sites should range from good (IRI < 95 in/mile) to acceptable (95-170 in/mile) to poor (>170 in/mile). At least one of the ASP sites should have rut depths exceeding 0.25 inches. At least one of the selected JCP sites should have fault heights greater than 0.25 inches present at joints. The JCP sites should also have the same tining patterns that are widespread throughout the network. Some of the sites should also have cracking and other distresses that are typical on the network. Finally, some of the sites should be longer and include curves, grades, and cross-slopes to allow geometric measurements to be validated.
Control site start and end locations must be marked by means of reflective tape on the pavement surface. This will facilitate consistent registration of the exact limits of collection, making comparisons of repeat runs possible. The start and end locations should additionally also be georeferenced by means of suitable survey equipment, and SHP files should be produced defining the limits and path of collection. This makes automated comparisons of collected data to the reference data possible.
Reference Data to be Collected
The types of reference data that should be collected on control sites must match the data types being collected by the equipment to be validated. At a minimum, control sites will validate IRI, rutting, faulting, and cracking since these data types are required for HPMS reporting purposes. Texture, geometrics, and friction data should also be validated if this data is being collected by or for the DOT.
Longitudinal Profile and Roughness (IRI)
Longitudinal profile is used to calculate the International Roughness Index (IRI), the most common metric of road performance. During equipment validation, it is important to compare the underlying longitudinal profile data to a reference, not just the IRI data. The IRI numbers, particularly when averaged over 0.1-mile intervals, can hide computational inaccuracies and equipment problems.
Collection of Reference Profile
The most accurate device for collecting reference profile data is the SurPRO. According to NCHRP Synthesis 526, the SurPRO is the most-used walking profiler by U.S. DOTs. It is also the most-referenced device in the academic literature. The SurPRO is repeatable to itself with cross-correlations exceeding 0.99.
Normally, it is sufficient to collect reference profile data with a SurPRO on one or two of the control sites only. A suitable high speed reference profiler can then be certified against the walking profiler on those one or two sites, and the reference profiler can then be used to establish the reference data for the other control sites.
Collecting reference data with a walking profiler requires road closure.
The walking profiler establishes a reference longitudinal profile, from which a reference IRI value is calculated for each site.
Transverse Profile and Rutting
Collection of Reference Data
Rut depths are measured with a physical straight-edge or wire every 1 m (3.28 ft) along the ASP control sites. The deepest rut depth is measured beneath the straight-edge or wire. The values are recorded along with the precise linear distance from the control site start location.
Collecting rutting reference data requires road closure.
Collection with High Resolution Device
High resolution transverse profiles and rut depths can optionally be collected with an LCMS-2 system. Transverse profiles can be optionally corrected for vehicle roll angle such that the resulting profile represents the road cross-slope accurately. With this method, transverse profiles and rut depths should be measured at very small intervals such as 1 inch intervals along the roadway.
The data collected by the reference LCMS-2 system should be validated against rut depths measured with a traditional method on at least one control site.
Joint Detection and Faulting
Collection of Reference Data
Reference joint locations and fault heights on JCP pavements can be collected using an ICC profiler tightly synchronized with an LCMS-2 system. The combination of two independent systems provides a higher degree of confidence that joint locations are detected automatically.
When establishing the control site, the exact count and location of joints along the control site is measured and visually verified. The fault heights are calculated in the wheelpaths and center at each joint.
Pavement Images and Distress
Collection with High Speed Device
Reference pavement imagery should be collected using the highest resolution 2D/3D pavement imaging system available, such as the LCMS-2. Three types of images are collected at 1mm by 1mm resolution: 3D range, 2D intensity, and 3D composite images. This imagery allows all road defects to be detected and measured accurately.
The reference distress data is usually based on an automated crack detection pass, with classification and rating according to the specified distress protocol. A detailed manual review of the images is performed and any distresses missed by the automated method are drawn manually. The distress data is then summarized for each control site, and the HPMS cracking percent values are also calculated. Care must be taken to summarize the data using a methodology that does not introduce addition variability. Binning of distress by severity should be avoided, for example, as it makes cracking data less repeatable near bin boundaries.
Collection of Reference Data
Texture data is measured using a high resolution device such as the Fast Texture Meter (FTM). This device measures the pavement surface profile throughout the macrotexture range, as well as partially in the microtexture range. From this profile data, the MPD and RMS values are calculated.
The reference data should be collected in the same wheelpath locations as texture will be collected by the high speed equipment. The device should log the GPS position of each measurement so they can be placed accurately within the control site and be compared to high speed equipment measurements at those locations.
Collecting texture reference data requires road closure.
Collection of Reference Data
Geometric properties of the road such as cross-slope (or cross-fall), grade, and curvature are important for safety. A complete calibration site setup should include reference measurements of geometric data.
The cross-slope of the road can be measured with a device such as the AccuSlope. Reference values are normally taken at 10 m intervals along the control site. The grade of the road is typically calculated from GPS elevation data and vehicle pitch angle captured by a reference vehicle equipped with an Applanix or iXBlue INS system.
The horizontal curvature of the road can be measured using the basic Compass Method, described here. For more accurate measurements, the curvature can be measured from GPS traces and vehicle heading angle collected by a reference vehicle equipped an Applanix or iXBlue INS system. The curvature can also be measured quite accurately from aerial imagery using GIS tools.