A Novel Motion Plane-Based Approach to Vehicle Speed Estimation

Speed limit violation by vehicles is one of the most frequent reasons for road crashes, which take the lives of many people every year, resulting in an increasing demand for video-based vehicle speed estimation systems. One of the biggest challenges to achieve monocular video-based vehicle speed estimation is the projection displacement difference (PDD) problem, where there is a plane disparity between street-level indicators and above-plane feature points of vehicles, thus resulting in unreliable speed estimates. In this paper, a novel motion plane-based approach for vehicle speed estimation is proposed, which addresses the problem of PDD. In the proposed method, we consider the center of a vehicle license plate as the vehicle reference point and estimate the hypothetical plane (named motion plane), on which license plate moves. Subsequently, the plate position is mapped on the motion plane and the displacement is then calculated, thus mitigating the effects of PPD. To estimate the motion plane, a texture-based shape-from-template technique is used. Unlike existing methods, the proposed method needs neither to apply any indicator nor to use any information about extrinsic parameters of the camera. Furthermore, since all the license plates are approximately located on a flat plane, the motion plane can be estimated by using several extracted 3-D points. Experimental results show that the proposed method performs better than the state-of-the-art vehicle speed estimation methods, illustrating the efficacy of this approach for achieving reliable vehicle speed estimation.