$3\mathrm{.}14$ A highway reconstruction project is being

undertaken to reduce crash rates. The reconstruction

involves a major realignment of the highway such that a

$60-m\frac{i}{h}$ design speed is attained. At one point on the

highway, a $720-ft$ equal$-$tangent crest vertical curve

exists. Measurements show that at $3+40$ stations from

the $PVC,$ the vertical curve offset is $3\mathrm{.}5ft.$ Assess the

adequacy of this existing curve in light of the

reconstruction design speed of $60m\frac{i}{h}$ and, if the

existing curve is inadequate, compute a satisfactory

curve length.