Estimating Velocity Fields on a Freeway from Low Resolution Video

We present an algorithm to estimate velocity fields from low resolution video recordings. The algorithm does not attempt to identify and track individual vehicles, nor does it attempt to estimate derivatives of the field of pixel intensities. Rather, we compress a frame by obtaining an intensity profile in each lane along the direction of traffic flow. The speed estimate is then computed by searching for a best matching profile in a frame at a later time. Because the algorithm does not need high quality images, it is directly applicable to a compressed format digital video stream, such as mpeg, from conventional traffic video cameras. We illustrate the procedure using a 15 minute long VHS recording to obtain speed estimates on a one mile stretch of highway I-80 in Berkeley, California.