Trailers, such as semi-trailers, having configurations that improve the aerodynamic efficiency thereof are provided. In some examples, aerodynamically configured trailers are provided that maintain standard cargo capacity. To improve the aerodynamic efficiency, the rearward end of the trailer in some embodiments include a downward cant or slope. In use, the rearward cant or slope reduces the low-pressure region that trails the end of the trailer, thereby reducing pressure drag. In accordance with another aspect, to accommodate loading and unloading of the downwardly canting or sloping trailer, examples of the trailers may also be equipped with “sliding trailer axle” and/or extended travel landing gear so as to allow the trailer to interface with standard loading dock heights as well as rampless ground loading/unloading.