Consider a 30,000-lb (133-kN) transit bus that has a single front axle load of
10,000 lb (44 kN) and a tandem rear axle load of 20,000 lb (89 kN). Before the ESAL
can be determined, the pavement thickness or structural number must be known, as
well as the terminal serviceability. In an initial design, this necessitates assumptions,
and very likely an iteration after the thickness or structural number has initially been
determined. In this example, the ESAL is to be determined for a rigid pavement 7 in
(178 mm) thick and for a flexible pavement with a pavement structural number of 4.
The pt is taken as 2.5. The tables show that, for this case, the equivalency factor for
rigid pavement is 0.089 for the front axle (Table 3.13) and 0.220 for the rear axle
(Table 3.14). The equivalency factor for flexible pavement is 0.102 for the front axle
(Table 3.4) and 0.141 for the rear axle (Table 3.5). Each bus equals 0.089 0.220
0.309 ESAL for rigid pavement and 0.102 0.141 0.243 ESAL for flexible pavement.
A similar analysis would be completed for each vehicle type. A worksheet for
making the calculations is provided in Table 3.19, and an example for using the worksheet
is presented in Table 3.20.