NREL's fleet test and evaluation team assesses the fuel savings potential of semi-automated truck platooning of line-haul sleeper cabs with modern aerodynamics. Platooning reduces aerodynamic drag by grouping vehicles together and safely decreasing the distance between them via electronic coupling, which allows multiple vehicles to accelerate or brake simultaneously. In 2014, the team conducted track testing of three SmartWay tractor - two platooned tractors and one control tractor?at varying steady-state speeds, following distances, and gross vehicle weights. While platooning improved fuel economy at all speeds, travel at 55 mph resulted in the best overall miles per gallon. The lead truck demonstrated fuel savings up to 5.3% while the trailing truck saved up to 9.7%. A number of conditions impact the savings attainable, including ambient temperature, distance between lead and trailing truck, and payload weight. Future studies may look at ways to optimize system fuel efficiency and emissions reductions.