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OCR for page 64
Chapter 3: Measurement difficulty exists in trying to define when a storm ends and when pavement has been restored to a bare condition. Once you settle on the definition of the measure, you need to compile or collect data to calculate it. If the data is unreliable or inaccurate and without an appropriate degree of statistical confidence, then the measure will be also unreliable or not accurate enough. Before you finalize the measures you will be using for benchmarking, you need to do a careful assessment of data availability, reliability, and accuracy. In addition, you need to estimate the costs of data collection. If the costs are excessive, you may have to choose another measure or accept a lower level of accuracy and confidence. You may think that there is too much emphasis on data and measurement quality. Many important decisions will eventually depend on the accuracy of the measures you collect and the underlying data; however, overemphasizing accuracy has its costs, too. Do not go overboard in trying to be too accurate. The right thing to do may be to start benchmarking and measuring as soon as possible and to gradually improve the quality of your measurements. A CATALOG OF MEASURES Appendix B provides a catalog of measures you may want to use for benchmarking. Many of the measures presented are widely used, and include those identified as "commonly recognized measures" at the national workshop on the topic. Some types of measures discussed are not yet widely used but are important from the standpoint of their relationship to the customer. As you get started with benchmarking, you will want to select among these and other possible measures. The catalog offers some guidance regarding the pertinence of each measure to the customer and its reliability, accuracy, and ease and cost of application. 66

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Performance measures are presented for the following areas: Pavements; Shoulders; Bridges; Signs, striping, and markings; Safety features; Ice and snow control; Roadside vegetation; Drainage; Litter removal; Rest areas; Signals; and Other electronic devices. As an example of the material in Appendix B; Table 2 (which is identical to Table B1) shows measures for pavements. Pavements experience different types of deterioration that affect their appearance, riding experience, and structural soundness. Table 2 presents the following information: Attributes important to the customer that the measure addresses; The name of the measure (e.g., IRI); Units of measurement (e.g., inches per mile); Commonly recognized at the National Workshop on Commonly Recognized Measures for Maintenance; Repeatable, reliable, and accurate--in other words, an assessment of whether the measure has these attributes; and Cost of using the measure or other important issues. 67

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Chapter 3: Measurement Table 2. Condition Measures for Pavements Commonly Repeatable, Recognized Cost and Other Attribute Measure Units Reliable, and by Issues Accurate? AASHTO? Pavement IRI Inches/mile Yes Well-established Low incremental Smoothness or m/km procedures and cost for agencies (roughness) equipment that result already in repeatable, reliable, collecting IRI; and reasonably moderate to high accurate results cost of new data collection effort Pavement NQI or other 15 response Survey Standard NQI survey Low cost to use Smoothness survey question scale question on question; not accurate NQI survey (customer asking customer pavement for jurisdictions lower results; satisfaction) satisfaction smoothness than state, unless moderate to high regarding separate survey cost to develop pavement administered and administer smoothness your own survey that includes question on pavement smoothness Pavement Number of Number per Potholes are easily High cost to Smoothness potholes of unit distance observed, but the develop a (potholes) specified size per number per unit comprehensive, unit distance distance can be accurate pothole difficult to count. The count. number of potholes can change rapidly as new ones appear and existing ones are repaired. Pavement Number of Number per Blowups are easily Seasonal Smoothness, blowups per unit unit distance observed and easy to problem that Accessibility distance count. Blowups occur requires (blowups) during the freeze-thaw moderate transition, so new measurement ones can suddenly cost; motorist emerge and affect the call-ins could reliability of the count. reduce data collection costs. Safety (danger of Rutting Inches Yes Well-established, Low cost to do hydroplaning) reliable, repeatable, for sample and reasonably sections or if accurate data already measurements using exists; high cost a ruler to obtain comprehensive coverage if data doesn't exist (continued on next page) 68

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Table 2. (Continued) Commonly Repeatable, Recognized Cost and Other Attribute Measure Units Reliable, and by Issues Accurate? AASHTO? Safety Friction Yes Well established Low incremental (skid resistance) equipment and cost if agency procedures for already routinely reliable, repeatable, measures; high and reasonably cost for new accurate measurement measures program Preservation Faulting Inches Repeatable, reliable, Low cost to do Characteristic and reasonably for sample (protection accurate measures sections or if against water obtained using ruler data already damage to exists; high cost structure due to to obtain faults) comprehensive coverage if data doesn't exist Preservation Extent and Percent of Challenge in Much lower cost Characteristic severity of area covered maintaining to do for sample (appearance of different types of or length of consistency among sections in deterioration, cracking: cracks and raters; automated comparison to raveling, water alligator rating of distress identification comprehensive infiltration) longitudinal severity on a technology not highly network transverse scale accurate coverage Overall Health Index Some type of Requires construction Low to high cost Pavement index, e.g., of index reflecting key to develop and Condition from 0100 pavement attributes; apply index, each characteristic depending upon can be measured with the availability of varying degrees of data to calculate reliability index components Overall Level of Visual Level of Rating scale Often visual rating Mainly useful for Service Service Condition of A, B, C, D, scales combine more communicating Rating or E than one to policy makers characteristic, and so and general it is difficult to portray public and isolate condition of different attributes 69