Disclosed are air rail assemblies for improved vehicle aerodynamics, methods for making and methods for using such air rail assemblies, and motor vehicles employing air rail assemblies for reducing turbulent flow and wake bubbles in and around the rear cargo bed. An air rail assembly for a motor vehicle is disclosed that includes an inlet port that extends through the rear quarter panel of a cargo bed sidewall. The inlet port intakes passing fore-aft airflow. An outlet port extends through a rail cap and ejects airflow intake from the cargo sidewall. An air duct, which attaches to an inboard surface of the rear quarter panel, fluidly connects the air inlet and outlet ports. The air duct includes transverse and vertical channels that cooperatively redirect the airflow intake in an inboard and upward direction. The air duct includes convergent portions that constrict and accelerate the airflow intake.