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C H A P T E R 2 Factors Affecting Project and Treatment Selections for Pavement Preservation There are many factors that affect the selection of a pavement- levels for rural and urban roadways. These plots were analyzed preservation project and treatment. For high-traffic-volume to determine at what ADT at least 50% of reporting agencies roadways in particular, the ability of the treatment to stand up were represented. As a result of the responses and the analy- to higher traffic volumes is certainly important. Other factors ses, it was determined that a reasonable definition of high also increase in importance as the desire to minimize owner traffic volume is 5,000 vpd for rural roadways and 10,000 vpd risk and disruption to the traveling public are considered. for urban roadways. This is described in greater detail in the These guidelines identify the following factors, which are project report. described in greater detail in the sections that follow: The high-traffic-volume classification levels provided by the responding highway agencies were also analyzed for trends Traffic levels; concerning preservation treatment use. According to survey Pavement condition; responses, crack sealing, followed by crack filling, cold milling, Climate/environment; and thin HMA overlays, are the treatments most extensively Work zone duration restrictions; used on both rural and urban HMA-surfaced roadways. Sim- Expected treatment performance; and ilarly, joint resealing, crack sealing, and diamond grinding Costs. are the treatments with the greatest use on rural and urban PCC pavements. At the opposite end, preservation treatments such as cape sealing, fog sealing, and diamond grooving are Traffic Level used infrequently on high-traffic-volume roads. Tables 2.1 The traffic level is important for at least two reasons: it is a and 2.2 summarize the use of preservation treatments on direct measure of the loadings applied to a roadway and it HMA- and PCC-surfaced roadways, respectively. From this, affects access to a roadway to perform preservation activities. the general practice of each treatment can be assessed accord- Traffic levels may also be indirectly related to an agency's risk ing to the traffic level of the roadway. tolerance: the higher the ADT, the less likely the agency is to In addition to determining the extent of treatment use, try a treatment that may not have a long life or, if it fails, may information was sought on which treatments are predomi- adversely affect many users. nantly used on high-traffic-volume roadways and whether One of the steps taken in developing these guidelines was there is a difference in strategies for treating rural roadways to arrive at a definition of "high"-traffic-volume roadways. as opposed to urban roadways. Overall, approximately 60% There is no national or American Association of State High- of agencies reported using a different set of treatments for way and Transportation Officials (AASHTO) definition of rural high-traffic-volume roadways versus rural low-traffic- high traffic volumes, probably because it is a local issue: volume roadways, whereas a slightly lower margin of the what one agency defines as high traffic volume could easily majority reported using a different set of treatments for be considered low traffic volume by another. To address this urban high-traffic-volume roadways versus urban low-traffic- variability, a survey of state highway agencies' (SHA) prac- volume roadways. However, there was little difference in treat- tices was conducted in which agencies were asked how they ment strategies between rural and urban high-traffic-volume defined low, medium, and high traffic on both rural and roadways. Tables 2.3 and 2.4 list the preservation treatments urban roadways. The responses were broken down using used by at least 50% of highway agencies on their rural and descriptive statistical analyses to plot histograms of ADT urban high-traffic-volume roadways. 4