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A_COM Pavement Management Loading Study <br />City of Santa Ana, California <br />Equivalent Single Axle Loadings <br />Roadway pavements are designed to carry the expected number of vehicle loadings over <br />the design life of the pavement. Vehicle loadings are determined based on the weight of the <br />vehicle and the number and type of axles on the vehicle. <br />The common axle types include single axles with two or four wheels; tandem axles, which <br />are two single axles mounted adjacent to each other; and tri- axles, which are three single <br />axles mounted together. Each vehicle has a different weight and trucks can have many <br />different axle combinations. For example, a straight (single unit) truck often has a single <br />axle in the front and a tandem axle in the back. A semitrailer truck often has a single axle in <br />the front, a tandem axle at the back of the tractor, and a tandem axle at the rear of the trailer <br />(18 wheeler). Other combinations are common. <br />In order to bring all the possible vehicle weights and axle combinations to a uniform number <br />to enable pavement design, the concept of Equivalent Single Axle Loading (ESAL) was <br />developed by AASHTO. An ESAL is one loaded pass of an 18,000 lb single axle. One <br />loading of one 18,000 lb single axle is considered a 1.0 load factor. Other combinations of <br />weights and axle combinations would have factors less than or greater than 1.0. Heavier <br />loadings would be greater than 1.0, while adding axles to make tandem and tri -axles would <br />result in lower load factors for a given weight. Knowing the actual axle types and weights on <br />those axles enables the total loading on the pavement to be calculated for each vehicle. <br />CalTrans has further calculated truck loadings and developed ESAL constants based on <br />truck types by axle classification and typical truck weights. This enables ESAL loadings to <br />be calculated from truck classification counts rather than actual weights. <br />The pavement loadings of heavier trucks are much greater than those of lighter vehicles. <br />Therefore, the damage to a pavement from each truck driving on it is much greater than <br />from each automobile. The following table summarizes the relative loading impact of cars <br />and trucks on a typical existing Santa Ana local residential street paved with hot mix asphalt. <br />AECOM Project No. 60477125 <br />65B -7 <br />June 21, 2016 <br />Page 3 of 11 <br />