Display time for a billboard message is varied in proportion to measured speed of one or more vehicles. This may include varying not only the time a message is presented on the billboard, but also varying the density of the message. An overall message may be broken into segments displayed a sequence of billboards depending on the speed, e.g., for a faster moving vehicle the message has more segments. If the speed of a vehicle is great enough, the message segments are also reduced to fewer words or graphics, which may also be larger. Also, clusters of vehicles are detected and a billboard message display is varied in response to the clusters, which may include display time or segmentation variation, so as to more nearly optimize the number of persons who are able to see the message. Further, a billboard is rotated per vehicle speed, distance, length or clusters.