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55 GLOSSARY Acceptance plan: An agreed-upon method of evaluating the without the benefit of automated equipment (e.g., visual acceptability of the pavement condition data. surveys and faultmeters) (6). Acceptance testing: The activities required to determine the Pavement condition: An evaluation of the degree of deteri- degree of compliance of the pavement data collected with oration and/or quality of service of an existing pavement contract requirements. section at a particular point in time, either from an engi- Accuracy: The degree to which a measurement, or the mean neering or user (driver) perspective. The condition as it is of a distribution of measurements, tends to coincide with perceived by the user is often referred to as functional con- the true population mean. When the true population mean dition. The estimated ability of the pavement to carry the is not known, as is the case with pavement data collection, load is referred to as structural condition. the degree of agreement between the observed measure- Pavement condition indicator: A measure of the condition ments and an accepted reference standard (ground truth) is of an existing pavement section at a particular point in typically used to quantify the accuracy of the measure- time. This indicator may be a specific measure of a pave- ments (16). ment condition characteristic (e.g., smoothens or cracking Automated data collection: Process of collecting pavement severity and/or extent) or an index defined for a single dis- condition data by the use of imaging technologies or other tress (e.g., cracking), for multiple distresses (e.g., Pavement sensor equipment (6). Condition Index), or for the overall pavement condition. Automated data processing: The reduction of pavement Pavement performance: The history of pavement condi- condition (surface distresses, such as cracking and patching, tion indicators over time or with increasing axle load or pavement condition indices, such as IRI) from images applications (16). or other sensors. The process is considered fully automated Precision: The degree of agreement among a randomly if the pavement condition (e.g., distresses) is identified and selected series of measurements of a particular characteris- quantified through techniques that require either no or very tic (or attribute) or the degree to which tests or measurements minimal human intervention (e.g., using digital recognition on identical samples tend to produce the same results (16). software capable of recognizing and quantifying cracks on Quality: "The degree to which a set of inherent characteristics a pavement surface) (6). fulfill requirements" (17). These requirements could be Bias: A systematic error, constant in direction, that causes a features and characteristics of a product that are specified measurement, or the mean of a distribution of measure- in a contract or identified and defined internally by the ments, to be offset from the true population mean (16). company/agency based on the customer expectations. The Calibration: A systematic process to validate a specific product could be a physical entity (e.g., a calculator) or a measurement technique and equipment by comparing the service (e.g., auto repair, or, as is the focus of this synthesis, measurements with a standard that is considered correct. data collection). This standard is commonly called "ground truth." Adjust- Quality acceptance: Those planned and systematic actions ment to the equipment or technique may be required to necessary to verify that the data meet the quality require- match the "correct" measurement. ments before they are accepted and used to support pave- Control site testing: The use of reference measurements on ment management decisions. These actions govern the specific pavement sections (with well-defined locations) to acceptance of the pavement condition data collected using assess the quality of a pavement condition data collection either a service provider or in-house resources. Quality process. If the location of the session is not known to the acceptance is often referred to as quality assurance in the data collection team, these are referred to as blind control pavement engineering and management field. sites or segments. Quality assurance: The part of quality management focusing Data processing: Covers all the activities that are conducted on increasing the ability to fulfill requirements. It includes all to convert the raw data collected in the field surveys to those planned and systematic actions necessary to provide useful information. confidence that a product or facility will perform satisfac- Ground truth: See "reference value." torily in service. Because this term is often used in practice Independent assurance: A management tool that requires to refer to quality acceptance activities, to avoid confusion a third party, not directly responsible for process control it is not used in the remainder of the synthesis. or acceptance, to provide an independent assessment of Quality audits: A quality audit is the process of systematic a product or service and/or the reliability of test results examination of a quality system carried out by an internal or obtained from process control and acceptance testing (16). external quality auditor or an audit team. It is a key element Manual data collection: Pavement condition data collection in the ISO quality system standard to verify that the institu- through processes where people are directly involved in tion has clearly defined internal quality monitoring proce- the observation or measurement of pavement properties dures linked to effective action.
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56 Quality control: Those actions and considerations necessary ments. Repeatability measures the ability of the equipment/ to assess and adjust production processes so as to control technology/raters to produce the same values on repeated the level of quality being produced in the end product. It is measurements. also called process control. For purposes of this synthesis, Reproducibility: The ability of a technology or equipment quality control activities are those used to control the to accurately reproduce or replicate measurements not in data collection activities, either by a data collection ser- the same section [adapted from Transportation Research vice provider or a road agency collecting data in-house, so Circular E-C037 (16)]. The reproducibility of pavement that quality pavement condition data can be obtained. condition measurements is typically measured as the stan- Quality control plan: A document that describes the process dard deviation of measurements taken with different equip- to be followed for delivering the level of pavement condi- ment or using different technologies. It is a measure of tion data quality required. This plan typically includes data how well two different devices/methods/raters are able to quality objectives (precision, accuracy, completeness, etc.), measure the same pavement condition value on the same organization and responsibility, sampling procedures, road segment(s). Reproducibility relates to the agreement equipment requirements (calibration, verification, etc.), pro- of test results with different operators, test devices, and/or cessing of the quality control data, statistical analysis to be testing conditions. conducted, reporting, documentation of potential problems, Semi-automated data processing: Process of collecting and remedial solutions. pavement condition data using imaging technologies or Quality management: The overarching system of policies other sensor equipment but involving significant human and procedures that govern the performance of quality input during the processing and/or recording of the data. control and acceptance activities; that is, the totality of the Time-history: A set of successive periodic measurements of effort to ensure quality in the pavement condition data. pavement condition over time on the same roadway sec- Quality system: The organizational structure, procedures, tions. This time-history can be used to determine pavement processes, and resources needed to implement quality performance. management to meet the quality objectives. Validation: The process of verifying the soundness or effec- Reference value/ground truth: A measurement of a pave- tiveness of a pavement data collection process thereby ment characteristic (or attribute) that is considered to be indicating official sanction. the "correct" measurement for this characteristic. Verification: The process of determining or testing the truth Repeatability: The variation in measurements taken by a or accuracy of pavement condition data collection by single piece of equipment on the same road segment(s) examining the data and/or providing objective evidence. and under the same conditions (over a short period of Verification sampling and testing may be part of an inde- time) [adapted from Transportation Research Circular pendent assurance program (to verify quality control and E-C037 (16)]. It is generally evaluated based on the stan- acceptance testing) or part of a pavement condition data dard deviation of repeated values from different measure- collection acceptance program.