At first glance, this equation looks quite complex – it is.
Where:  W  =  axle applications inverse of equivalency factors (where W_{18} = number of 18,000 lb (80 kN) single axle loads) 
L_{x}  =  axle load being evaluated (kips)  
L_{18}  =  18 (standard axle load in kips)  
L_{2}  =  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  =  a function of the ratio of loss in serviceability at time, t, to the potential loss taken at a point where p_{t} = 1.5  
p_{t}  =  “terminal” serviceability index (point at which the pavement is considered to be at the end of its useful life)  
b  =  function which determines the relationship between serviceability and axle load applications D = Slab Depth in inches 
Example Calculation
 Assumptions: Single axle, 30,000 lb (133 kN), D = 7 in., p_{t} = 2.5
 Answer: (Table D.13, p. D15, 1993 AASHTO Guide) = 7.7
 Calculations
where :  W_{18 }  =  predicted number of 18,000 lb (80 kN) single axle load applications 
W_{30}  =  predicted number of 30,000 lb (133 kN) single axle load applications  
L_{x}  =  L_{30} = 30  
L_{2x}  =  1 (single axle)  
G  =  serviceability loss factor  
=  
b_{30}  =  curve slope factor  
=  
and  G/b_{30}  =  0.1761/5.7298 = 0.03073 
b_{18}  =  
G/b_{18}  =  0.1761/1.3709 = 0.12845  
Thus,  
and  of W_{18} loads allowable with a 30,000 lb. single axle  
Finally,  LEF  =  (same as contained in 1993 AASHTO Guide âcol Appendix D) 