1. A method for vehicle detection and tracking, comprising: acquiring video data including a plurality of frames; comparing a first frame of the acquired video data against a set of one or more vehicle detectors to form vehicle hypotheses; pruning and verifying the vehicle hypotheses using a set of coarse-to-fine constraints to detect a vehicle; and tracking the detected vehicle within one or more subsequent frames of the acquired video data by fusing shape template matching with one or more vehicle detectors, wherein the set of coarse-to-fine constraints includes a first level in which an objective function is replaced by a course approximation and a second level in which mode locations obtained in the first level are refined by optimizing the objective function.