Equivalent Standard Axle Load

The Classical Mechanistic-Empirical method makes use of an Equivalent Standard Axle Load (ESAL). This is a 40 kN dual wheel load with a tire pressure of 0.69 MPa and centre distance between the tires of 300 mm (although this may be changed in the table "Wheels" in the database).

The actual wheel load spectrum read from the WIM data is converted to ESALs using a power of 4.2 (this can be changed in the "Limits" table of the database).

The total number of ESALs during the design life is calculated from the number of axle passages during the first year and the growth rate in percent. If desired the number of ESALs may also be calculated from the TI, using the Caltrans design method.