A trailer with a bogie assembly , said trailer comprising: a top fairing configured for being mounted to a top surface of the trailer , wherein the trailer has a longitudinal direction , a lateral direction , and a vertical direction , wherein the top fairing is configured to be located closer to the back of the trailer than to the front of the trailer in the longitudinal direction , wherein airflow across the top fairing in the longitudinal direction is over an upper surface of the top fairing and there is no or negligible airflow in the longitudinal direction between the top fairing and the top surface of the trailer , wherein the airflow across the upper surface of the top fairing in the longitudinal direction moves upward in the vertical direction and then subsequently downward in the vertical direction , a first trailer skirt configured to be carried by the trailer ; a second trailer skirt configured to be carried by the trailer ; a first trailer rear skirt configured to be located rearward of the first trailer skirt in the longitudinal direction , wherein the first trailer rear skirt and the first trailer skirt are configured to be located closer to a first side surface of the trailer than to a second side surface of the trailer in the lateral direction ; and a second trailer rear skirt configured to be located rearward of the second trailer skirt in the longitudinal direction , wherein the second trailer rear skirt and the second trailer skirt are configured to be located closer to a second side surface of the trailer than to a first side surface of the trailer in the lateral direction , characterized in that the bogie assembly of the trailer is movable in the longitudinal direction relative to the first and second trailer rear skirts, wherein the bogie assembly is moveable such that at least a portion of the bogie assembly is positioned rearward of leading forward ends of the first and second trailer skirts in the longitudinal direction . a top fairing configured for being mounted to a top surface of the trailer , wherein the trailer has a longitudinal direction , a lateral direction , and a vertical direction , wherein the top fairing is configured to be located closer to the back of the trailer than to the front of the trailer in the longitudinal direction , wherein airflow across the top fairing in the longitudinal direction is over an upper surface of the top fairing and there is no or negligible airflow in the longitudinal direction between the top fairing and the top surface of the trailer , wherein the airflow across the upper surface of the top fairing in the longitudinal direction moves upward in the vertical direction and then subsequently downward in the vertical direction , a first trailer skirt configured to be carried by the trailer ; a second trailer skirt configured to be carried by the trailer ; a first trailer rear skirt configured to be located rearward of the first trailer skirt in the longitudinal direction , wherein the first trailer rear skirt and the first trailer skirt are configured to be located closer to a first side surface of the trailer than to a second side surface of the trailer in the lateral direction ; and a second trailer rear skirt configured to be located rearward of the second trailer skirt in the longitudinal direction , wherein the second trailer rear skirt and the second trailer skirt are configured to be located closer to a second side surface of the trailer than to a first side surface of the trailer in the lateral direction , <EOS>