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_ 1~ , <br />(<X~ ~~ lT ' l.." ~ ~~tnu~ clC.~ i n e ~r{l~ tks i~o.wd' LtSR~ ~SphosTQaV2n~.~s er ~JoraC(O II <br />~~ys <br />In this Design Guide, pavement section thickness is determined using the following information: <br />• Subgrade strength, Resilient Modulus (MR) <br />• Traftic analysis, ESALs <br />• Desired reliability level of pavement performance <br />• Drainage characteristics <br />• Structural Number, SN <br />In ChapterThree, strength coefficients are provided for various types of materials available for use <br />in the pavement section. Chapter Three also provides thickness design procedures for <br />determining alternate pavement sections. <br />TRAFFIC ANALYSIS ~ r~.~T~~ G~~~`=' ~~ ~~'~~P-c~-`''`"~~'Y ~~° ~ J <br />Because the primary function of a pavement is to transmit and distribute wheel loads of vehicles <br />to the supporting subgrade, information about the traffic stream is required. Pavement should be <br />designed to serve traffic needs over a period of years. The volume of traffic and the various types <br />of vehicles using the facility should be estimated for the pavement's anticipated performance <br />period. <br />A traffic assessment for an existing roadway, that is going to be improved, should be based on a <br />detailed traffic count of the existing traffic. The existing traffic should be determined for the <br />following three categories: <br />1) Passenger cars and pickup trucks. <br />2) Single unit trucks. <br />3) Combination trucks. <br />Anticipated changes in traffic type should also be <br />considered. Based on appropriate growth factors, <br />the traffic volume is projected or inflated out to the <br />end of the performance period, usually 20 years. <br />Local agencies should also consider the type and <br />extent of construction traffic loads in new <br />developments. Most often, the heaviest loadings <br />occur during the build-out phase of the <br />development. If these loadings are not taken into <br />account in the pavement structure design, a <br />shortened performance period of the pavement structure could result. <br />Since pavements are usually designed for periods ranging up to 20 years on the average or more, <br />it is necessary to predict the ESAL's for this period of time, i.e., the performance period. The <br />performance period, often referred to as the design period, is defined as the period of time that <br />an initial pavement structure will last before reaching its terminal serviceability. Any performance <br />period may be used with this Guide since design is based on the total number of equivalent single <br />axle loads (ESAL's). However, experience may indicate a practical upper {imit based on <br />considerations otherthan traffic. The ESAL's for the performance period representthe cumulative <br />number from the time the roadway is opened to traffic to the time when the serviceability is <br /> <br />