A tractor-trailer rig has frontal area \(A=102 \mathrm{ft}^{2}\) and drag coefficient \(C_{D}=0.9\). Rolling resistance is \(6 \mathrm{lbf}\) per \(1000 \mathrm{lbf}\) of vehicle weight. The specific fuel consumption of the diesel engine is 0.34 \(\mathrm{lbm}\) of fuel per horsepower hour, and drivetrain efficiency is 92 percent. The density of diesel fuel is \(6.9 \mathrm{lbm} / \mathrm{gal}\). Estimate the fuel economy of the rig at \(55 \mathrm{mph}\) if its gross weight is 72,000 lbf. An air fairing system reduces aerodynamic drag 15 percent. The truck travels 120,000 miles per year. Calculate the fuel saved per year by the roof fairing.