Interest in the aerodynamics of ground vehicles has been revived onlyrecently. This is due to the explosive increase in the nwnber of ground vehiclesin operation as well as the serious concern about future availability of energyfor massive scale vehicle operation. Vehicle aerodynamics encompasses abroad class of phenomena which result from the flow field generated aroundthe vehicle during its motion. This is governed by the vehicle shape, magnitudeand direction of ambient wind, terrain characteristics and mutual interferencewith other vehicles, etc. Apart from the external flow field, there are two othertypes of internal flows; engine cooling and passenger compartment airconditioning.This work is limited to the external flow around road vehicles andfurnishes a theoretical and an experimental study for one of the most importantapplications of aerodynamics. The thesis is divided into two parts; the first oneis the experimental work and the second is the theoretical work.1- Theoretical Work:A computer code capable for handling the three-dimensional turbulentflow around the models was designed. For this study, two turbulence models;constant viscosity and energy-dissipation, were considered. Computations werecarried out in the central computer (V AX 6510 working under VMS V.5.5operating system) of the FRCU (Foreign Relations Coordination Unit), CairoUniversity. We used the finite volume technique in developing this code takinginto consideration the following factors:1- Change of speed of vehicle2- Gap distance between cabin and load.3- Opening the windows of a bus ill motion.4- Side wind.S- Add-on-devices.These parameters-to the best of my knowledge-have not beentheoretically examined before. The pressure distribution as well as pressurecontours and velocity contours and vectors at various planes perpendicular andparallel to the plane of symmetry of the vehicle were plotted. The dragcoefficient was also calculated.2- Experimental WorkFour models were fabricated to a scale of 1:10. These models are:-1- Mitsubishi passenger car (fastback)Regata passenger car (notchback)