Aerodynamic streamlining of commercial vehicles is believed to both improve fuel efficiency, by reducing aerodynamic drag, and reduce the dispersion of water spray by limiting the extent of the vehicles' external air flow field. Measurements of drag from a programme of wind tunnel model experiments are presented in this report, showing the effect of different tractors and of a variety of streamlining devices. Pressures on the box trailer were measured on models in the wind tunnel and at full scale during road and track tests. These were used to assess the validity of the model tests. Propagation of spray around the vehicles was assessed subjectively by studying smoke flow beside and behind the models in the wind tunnel. Aerodynamic devices that reduced the drag of the vehicles tended to reduce the area around the vehicles that appeared to be affected by spray. Streamlining the goods vehicles increased the pressure differences along the sides of the trailer box body. This has implications for the strength of curtain-sided box vehicles, and probably indicates that streamlining does not reduce the aerodynamic forces on other vehicles travelling close to or overtaking the box vehicle.

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