Aerodynamic Drag Reduction of Intercity Buses

An experimental program was conducted to verify the reduction in fuel consumption achievable with aerodynamic improvements to intercity buses. Wind tunnel model tests were used to develop effective aerodynamic improvements and full-scale road tests to validate the results. Greyhound Lines coach models MC-7 and MC-8 were tested with head- and crosswinds. Aerodynamic drag of the MC-7 was reduced 17 percent at zero yaw. Drag of the MC-8 initially was higher; it was reduced 27 percent at zero yaw by the best fairing. Both low-drag configurations were less sensitive to crosswinds than the original models; significant drag reduction was maintained to 15 degrees yaw angle. Fuel consumption measurements made with aerodynamic fairings installed on an MC-7 showed that the low-drag bus used 11.7 percent less fuel at a steady 55 mph. The cost of the full-scale modifications was estimated at $ 1,500 each for a retrofit kit and no added cost to produce on new vehicles. Return on investment for the aerodynamic improvement exceeds 100 percent annually for today's fuel costs.