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4 2.2 Traffic Characteristics 2.3.2 Gradient/Curves The traffic volume and type of traffic affect the selection of Steep inclines and curves may adversely affect performance materials used on chip seals. Generally, higher traffic volume due to tractive forces and slower moving vehicles. Therefore, and a higher percentage of heavy trucks on an undivided road- traffic control may need to remain in place until the emulsion way present a greater likelihood for vehicle damage if traffic is has cured sufficiently to retain the chips. not adequately controlled during construction. In addition, the volume and type of the traffic are directly related to the poten- 2.3.3 Intersections tial for chip embedment in the substrate. Also, traffic accelera- tion affects chip-seal performance as chips are more likely to be Turning, acceleration, and deceleration can cause chip loss dislodged under these loads than at constant speeds, which can and flushing. Therefore, traffic control may need to remain in lead to flushing and bleeding of the surface. This section dis- place until the emulsion has cured sufficiently to retain the chips. cusses the factors that influence the material's selection process depending on traffic volume, type of traffic, and speeds. 2.3.4 Width Vehicle movement tends to be more concentrated on nar- 2.2.1 Chip Selection row, secondary roads than on wider primary facilities. This results in a greater tendency for flushing in the wheel paths Larger chips provide more tolerance for emulsion applica- on these types of pavements. tion variance and are less likely to become totally embedded by traffic if the substrate is resistant to embedment. Larger chips require higher emulsion application rates for proper 2.4 Highway, Residential, Urban, embedment, thus increasing the sealing ability of the chip or Rural seal. However, large chips are noisier and provide higher risk 2.4.1 Highway of vehicular damage during construction. Chip seals can be successfully constructed on highways with over 7,500 vehicles per day per lane with little or no 2.2.2 Emulsion Selection consequences with respect to vehicle damage (Shuler 1991) Emulsions modified with elastomeric polymers provide if important principles are followed. However, other fac- higher adhesion for aggregate chips, often both during con- tors should be considered regarding the use of chip seals on struction and later in the life of the seal. Also, research (Shuler high traffic highway pavements. Because noise increases with 1991) indicates that on high traffic facilities (i.e., greater than increasing traffic volume and chip size, smaller aggregates 7,500 vehicles per day per lane), modified asphalt emulsions are often desired for high traffic facilities. However, more are required to hold chips in place due to reduced emulsion accuracy relative to emulsion spray rate is needed when using application rates that are necessary to reduce the potential for smaller aggregates because the smaller embedment depth embedment in the substrate and consequent flushing. increases the potential for chip loss. 2.2.3 Fog Seal 2.4.2 Residential The application of a fog seal over a fresh chip seal provides Chip seals constructed with larger aggregates are rough high color contrast that improves visibility of striping, and textured. This rough surface texture is often unpopular among short-term performance improvement (Shuler 2007). Care residential users such as roller skaters and skateboarders or should be taken whenever applying a fog seal since pavement individuals who need to lie on the pavement to repair vehicles. friction could be reduced if the fog seal is applied at too high an application rate, the fog seal emulsion has a high residue 2.4.3 Rural content, or the fog seal has not broken sufficiently to support uncontrolled traffic. Rural settings are the most appropriate for chip seals. Traf- fic tends to move more consistently with less stopping and starting, and volumes are often lower, creating wider vehicle 2.3 Geometry separation providing less possibility for vehicle damage. 2.3.1 Divided/Undivided 2.4.4 Urban Divided alignments generally reduce the possibility for vehicle damage caused by loose, flying chips because of the Urban environments are often the most challenging envi- separation of opposing traffic. ronment for chip seals because of the higher traffic volumes