The Experimental Study of the Air Flow Produced by Road Vehicles and its Potential Destabilizing Effect on Nearby Pedestrians

The air movement produced by various types of road vehicles has been experimentally determined in order to evaluate the potential of this air flow to destabilize nearby pedestrians. Six vehicles are used, as small as an automobile and as large as a tractor-trailer combination, driven at speeds ranging from 20 to 50 mph (23 to 80 kph), at distances to sensors of two to six feet (0.6 to 1.8 m), in order to quantify some of the chaotic effects of the air motion generated by these vehicles, and specifically, what destabilizing effect it can have on nearby pedestrians. For each combination of testing variables, the peak air speed, relative temporal gust occurrence, and settling time to ambient conditions were measured. The results are analyzed, and a discussion is provided regarding the relation of factors, such as vehicle speed and the distance to the speed sensor, to the magnitude of the maximum air speed recorded. For all tests and conditions, the maximum vehicle-induced air speed was measured to be 25.3 mph (40.7 kph), and that was observed during a test with a cab-over tractor attached to a semi-trailer. It was determined that the vehicle-induced air speeds increased as vehicle speeds increased and as the sizes of the vehicles increased. It was found that the variations in vehicle-induced air speed are not explained by the distance from the side of the passing vehicle, within the tested distance range.