At first glance, this equation looks quite complex – it is.
Where:  W  equals  axle applications inverse of equivalency factors (where W18 = number of 18,000 lb (80 kN) single axle loads) 
L_{x}  equals  axle load being evaluated (kips)  
L_{18}  equals  18 (standard axle load in kips)  
L_{2}  equals  code for axle configuration 1 = single axle 2 = tandem axle 3 = triple axle (added in the 1986 AASHTO Guide) x = axle load equivalency factor being evaluated s = code for standard axle = 1 (single axle) 

G  equals  a function of the ratio of loss in serviceability at time, t, to the potential loss taken at a point where pt = 1.5  
P_{t}  equals  "terminal" serviceability index (point at which the pavement is considered to be at the end of its useful life)  
b  equals  function which determines the relationship between serviceability and axle load applications  
SN  equals  structural number 
Example Calculation for a Single Axle
 Assumptions: Single axle, 30,000 lb (133 kN), SN = 3, p_{t} = 2.5
 Answer: (Table D.4, p. D6, 1993 AASHTO Guide) = 7.9
 Calculations
where :  W_{18}  equals  predicted number of 18,000 lb (80 kN) single axle load applications 
W_{30}  equals  predicted number of 30,000 lb (133 kN) single axle load applications  
L_{x}  equals  L30 = 30  
L_{2x}  equals  1 (single axle)  
G  equals  serviceability loss factor  
equals  
b_{30}  equals  curve slope factor  
equals  
and  G/b_{30}  equals  0.2009/4.388 = 0.04578 
b_{18}  equals  
G/b_{18}  equals  0.2009/1.2204 = 0.1646  
Thus  
and  
Finally  LEF  equals  (same as contained in 1993 AASHTO Guide, Appendix D) 
Example Calculation for a Tandem Axle
 Assumptions: Tandem axle, 40,000 lb (133 kN), SN = 5, p_{t} = 2.5
 Answer: (Table D.5, p. D7, 1993 AASHTO Guide) = 2.08
 Calculations
where :  L40  equals  40 (tandem axle) 
L18  equals  18 (single axle)  
L2x  equals  2 (tandem axle)  
L2s  equals  1 (single axle)  
G  equals  serviceability loss factor  
equals  
b40  equals  curve slope factor  
equals  
and  G/b40  equals  0.2009/0.53824 = 0.37325 
b18  equals  
G/b18  equals  0.2009/0.50006 = 0.40175  
Thus  
Finally  LEF  equals  (same as contained in 1993 AASHTO Guide nbsp;Appendix D) 