In this paper, a calibration procedure for a single camera overlooking traffic is described. This procedure does not require the technician to measure any corresponding points or use special calibration targets. The technician installing the system simply measures the height and tilt of the camera and selects the road edges in an image. From these inputs, we use the vanishing point to compute the focal length and pan of the camera. We show that, using the calibration parameters, the projection equations can measure distances and speeds of vehicles within 1-2%.