1. A method for counting multiple passing vehicles in transition zones or entrances or exits of a multi-story carpark in a given direction along a two-lane two-way traffic road beneath a low clearance ceiling of the carpark, the method comprising: providing a video camera for producing a video stream, the video camera including a wide angle rectilinear lens forming a pyramidal view volume of the video camera, the pyramidal view volume having a field of view and four outer faces; locating the video camera at the ceiling above a road side edge so as to image the road across the field of view and align one of the faces of the pyramidal view volume parallel to the road side edge and perpendicular to the road; processing the video stream to model a prevailing background model of the road in the field of view; defining a rectangular monitor zone extending across the road; deriving a smoothed incident image for the rectangular monitor zone; and performing directional gradient processing on the smoothed incident image to produce a foreground image, comprising the steps of: convolving the smoothed incident image with Sobel horizontal and vertical kernels to produce horizontal and vertical gradient images, respectively; computing a gradient magnitude image from the horizontal and vertical gradient images; computing an adaptive suppression threshold for suppressing noise in the gradient magnitude image; comparing the smoothed incident image to the prevailing background model on a pixel-by-pixel basis; and producing the foreground image in response to determining a gradient orientation conformance between the smoothed incident image and the prevailing background model and in response to determining an intensity differential between the smoothed incident image and the prevailing background model; deriving a motion direction from a temporal change in the foreground image; and altering a vehicle count in response to deriving a motion direction.