$4\mathrm{.}4\mathrm{.}2$ Flexible$-$Pavement Design Equation

$lo{g}_{10}{W}_{18}=Z_R{S}_0+9\mathrm{.}36[lo{g}_{10}(SN+1)]-0\mathrm{.}20+\frac{lo{g}_{10}[\frac{}{P}SI\frac{?}{2\mathrm{.}7}]}{0\mathrm{.}40+[\frac{1094}{(SN+1{)}^{5\mathrm{.}19}}]}$

$+2\mathrm{.}32lo{g}_{10}{M}_R-8\mathrm{.}07$

Where:

$W_{18}=18-$kip$-$equivalent single$-$axle load,

$Z_R=$ reliability $(z-$statistic from the standard normal curve$),$

$S_0=$ overall standard deviation of traffic,

$SN=$ structural number,

$\frac{\frac{?}{{?}_{\frac{?}{?}}}}{P}SI=$ loss in serviceability from when the pavement is new until it reaches its TSI, and

$M_R=$ soil resilient modulus of the subgrade in $1\frac{b}{i}{n}^2.$

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