Abstract: A drag reducing device adapted to be mounted on the roof of the cab portion of a land vehicle including a trailing body for reducing aerodynamic drag. The device comprises a streamlined fairing including a bottom portion, a rear portion, and a continuous contoured surface extending widthwise and upwards from the bottom portion at the front of the fairing to the rear portion. The contoured surface has a top portion and side portions on either side of the longitudinal axis of the fairing which abut at their respective boundaries. The top portion has at least a substantially horizontal segment the tangential plane of which is inclined with respect to the horizontal at an angle which is at least equal to zero. The side portions diverge with respect to each other toward the rear portion and have substantially vertical segments which diverge with respect to the longitudinal axis of the fairing at an angle which is at least zero.