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C H A P T E R 1 Introduction Background Greater liability associated with failure; Negative public perceptions associated with certain treat- Since the early to mid-1990s, pavement preservation has grown ments; from an obscure term to standard practice in most highway Increased performance expectations; and agencies. Each practitioner may approach this from a different Lack of agency experience. vantage point, but at various times the driving forces behind this shift have included one or more of the following: The result is that where one agency will not use a certain treatment on pavements with average daily traffic (ADT) above A desire to improve overall pavement performance; 1,500 vehicles/day (vpd), another agency uses the same treat- Greater attention to customer satisfaction; ment routinely on pavements with ADT up to 20,000 vpd and Rising rehabilitation costs and constrained budgets; and higher. A need to improve safety in a cost-effective manner. None of these barriers is insurmountable, but each requires a targeted effort to address and overcome. A part of that effort Many agencies associate preservation with commonly used is addressed in SHRP 2 Renewal Project R26: Preservation preventive maintenance treatments. As such, treatments such Approaches for High-Traffic-Volume Roadways. A primary as chip seals or seal coats, crack filling, and slurry seals are objective of the project is to improve pavement preservation synonymous with pavement preservation. Furthermore, these practices on high-traffic-volume roadways. One way that same treatments are almost always used on lower-volume objective is being met is in the development of guidelines roads. Inevitably, a strong link has developed between pave- that can be used to preserve high-volume roadways in ser- ment preservation, preventive maintenance, and low-volume viceable condition for longer periods of time, at a lower cost, roads, even if it is purely circumstantial. in a safer manner, and with limited disruption to the traveling Nothing intrinsically limits pavement preservation to lower- public. volume roads, however. In terms of pavement performance, the same nonload factors that contribute to the deterioration of low-volume roads contribute to the deterioration of high- Purpose volume roadways. Similarly, most preservation treatments The purpose of these guidelines is to provide direction to agen- will have the same beneficial effects on a pavement regardless cies on the selection and use of preservation treatments for of traffic volumes. Even though higher traffic volume will high-traffic-volume roadways. These guidelines are based in have more effect on the structural aspect of the pavement, large part on agency experience and practice, as provided in preservation will slow or retard the structural deterioration. response to a detailed survey of practice and supplemented by At the same time, it is recognized that there exist barriers to the current practices gleaned from collected literature. It is greater use of preservation treatments on high-traffic-volume expected that agencies using these guidelines will be able to roadways. Among these barriers are the following: extend their use of pavement preservation on high-traffic- volume roadways through a greater familiarity with the Shorter available construction windows; described treatments. Increased risk of failure associated with durability of treat- Users of these guidelines should be aware that achieving the ment under higher traffic volume; desired results from pavement preservation is dependent upon 1