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61 CHAPTER NINE BEST PRACTICE CASE STUDIES INTRODUCTION to 20,000 lane miles per year at an average cost of about $2.6 million annually. Most use both in-house and contract On the basis of the survey responses, case studies were iden- crews to apply their chip seals and achieve satisfactory tified to detail findings that have the potential to disseminate results with both types of crews, although 10 of 13 agencies chip seal best practice in a timely manner. Each of the case believe that in-house seals produce a better final result. studies was drawn from a best practice case study form, which was sent to those survey respondents indicating the The major distress observed with the in-house chip seals performance of their chip seals as "excellent." This chapter is bleeding, especially at intersections, and the major distress first looks at those factors that the agencies with excellent observed with contract chip seals is early loss of aggregate. results have in common with regard to their chip seal proce- This finding makes sense, because chip seal contractors will dures and processes. Then it presents the salient elements of have a strong incentive to maximize production rates that individual responses for representative programs in a stan- may lead to less attention being given to achieving adequate dard format, permitting the reader to compare and contrast embedment. the various programs. Design and Material Selection COMMON CHARACTERISTICS OF EXCELLENT CHIP SEAL PROGRAMS All but one of the best practice case study agencies formally design their chip seals (including empirical design usage The following respondents reported that they achieve excel- based on past experience), and they use a procedure that has lent results from their chip seal programs. Their responses been in use for an average of 21 years. Eight respondents were separated from those of respondents in general for addi- entrust the design to their own maintenance engineers, using tional analysis. qualitative design input factors to develop the design. All use modified binders, with polymers and crumb rubber being the Arkansas State Highway and Transportation Department; most common modifiers. These agencies also select roads Colorado DOT--Alamosa, Grand Junction, Montrose, that have a distress level rated at moderate or less and whose Sterling, and Trinidad; structural cross section is rated as fair or better. They use Idaho Transportation Department; some type of pavement condition rating as the trigger point Nevada DOT; to consider the selection of chip seals for extending the life Oklahoma DOT; of the pavement. This finding is highly significant, in that as Texas DOT--Austin District; a group, the agencies demonstrate their understanding of WSDOT; both the advantages and limitations of chip seal technology. Austin, Texas; and In other words, they are "putting the right seal on the right Lubbock, Texas. road at the right time" (Galehouse 2003). The most striking factor among just those respondents that rated their chip seal program results as excellent is that Contracting and Construction all responded that they use chip seals as a PM tool by fol- lowing a specific PM cycle. Those agencies reported that The group's chip seal season typically runs from May to they typically use a 5-year PM cycle and expect to get a September, and they use unit-price contracts. They gener- 6-year service life from their seals. These two numbers are ally are not concerned about restricting chip seals to roads significant in that the planned PM cycle is shorter than the with low-volume traffic, with 11 of the 13 agencies chip expected life of the chip seal. This confirms that these agen- sealing roads having ADT of more than 5,000 vehicles, cies are truly committed to using chips seal as a pavement including 3 agencies that use chip seals on roads with preservation technique. Their level of confidence is further ADTs greater than 20,000 vehicles. The agencies appear confirmed, because they have an average of 7,000 lane miles to be interested in keeping up to date with the state of the of sealed pavement surfaces (DOT district level for all but art in chip seal construction equipment, as evidenced by the two cities), and that they do chip sealing on a range of 150 the knowledge that most require computerized controls on