QUESTION $6$:

A flexible pavement for an urban interstate highway is to be designed using the $1993$AASHTO guide procedure. You are the Pavement design engineer on this project and are required to determine a suitable pavement structure. Below are some of your identified necessary data for design:LayerCBRLayer CoefficientModulus of Resilience MrAsphalt Concrete$-0\mathrm{.}44450,000$lb$//$in$^(2)$ at $68$F$^($@$)$Base course$1000\mathrm{.}1431,000$lb$//$in$^(2)$Sub$-$base$220\mathrm{.}1013,500$lb$//$in$^(2)$

a$)$ What does the lane distribution factor account for?

$[2$ marks$]$

b$)$ Design a suitable Asphalt Concrete $($AC$)$ surfaced Pavement Structure with each layer thickness as a multiple of $2.$Give your pavement layer thicknesses in inches.

$[18$ marks$]$