A substantially flat fronted vehicle (10) such as a truck is provided with adjustable air deflector blades (24A-24D). The air deflector blades (24A-24D) provide upper (24A 24C) and lower (24B 24D) air deflector blades vertically mounted above one another and providing a gap (32) around the windscreen (8). The air deflector blades (24A-24D) are arcuate sheets in form and each supported by support arms (26) comprising vertically hinged first (38) and second (40) connected spring loaded arms that are urged to spring open but are held a selected angle and distance from the vehicle (10) front face (22) by wire rope length selection means and are thusly adjusted to promote least aerodynamic drag. Use on rail vehicles is also included. The apparatus has the unexpected effect of actually reducing forward vehicle aerodynamic drag in the presence of crosswinds.