# Derivation of the AASHTO formula of interior girder moment

The interior girder moment formula for one lane loaded for the AASHTO LRFD method is:

\begin{align} mg^{SI}_{moment}&=\left(1.75+\frac{S}{3.6}\right)\left(\frac{1}{L}\right)^{0.35}\left(\frac{1}{N_c}\right)^{0.45} \\ &= \left(1.75+\frac{13}{3.6}\right)\left(\frac{1}{100}\right)^{0.35}\left(\frac{1}{3}\right)^{0.45} \\ &= 0.65\ \mathrm{lane/web} \end{align}

How is this formula derived? I have not been able to find the original research paper.