Design a freeway pavement structure in an urban area for 20 years. An initial annual traffic is 250,000 EASLs and no annual growth factor is considered during design periods. A pavement structure shall comprise of three layers on top of a soil subgrade: HMA surface layer, Base layer with dense-graded crushed stone, and a subbase layer with crushed stone. Assume that the reliability and standard deviation are 90% and 0.30, respectively. The following additional information is available:

• All drainage coefficients = 1.2

• Modulus of HMA at 68 °F is 2.5x105 psi

• Modulus of base layer is 4x104 psi

• Modulus of subbase layer material is 1x104 psi

• CBR value of subgrade materials = 4

• Initial serviceability, pi=4.5 and terminal serviceability, pt=2.5

• Resilient modulus of soil (lb/in2)= 1500 x CBR

• Determine layer thicknesses (round up to nearest 0.5 in.) using AASHTO chart in the following page.