Print media allows the use of attention getting graphics.
Radio allows music or jingles and of course TV provides both visual as well as auditory stimuli.
Sure you may get an occasional person who walks behind it, but you are not accomplishing your purpose. The bottom line on any advertising campaign is to design your ad so that it gets attention. Classified Ads in the Newspaper are a good place to start in designing your online ad. In order to do this, you will have to examine the classifieds for a few days. Which ones run day after day and are really commercial in nature.