Generally, $15$ killovolt cables may be installed in Type RMC conduit with a

$5$ politis depth to the top of the conduit of only six inches. However, if the same conduit crosses under a vehicle traffic area, such as a road or a thoroughfare, the depth to the top of the conduit is increased to $?$

$15$

$12$

$24$

${18}^{**}$