Roadside turnouts on divided highways are a textbook example of applied freewayblogging strategy. Simply pull over on turnout, drive to the far end and place your sign so that it faces the oncoming lanes. Remember, if you can see their windshields from the posting spot, they can see your sign. The amount of time you can see their windshield is the amount of time they can see your sign as well.
To maximize duration, make sure your sign is hidden from forthcoming traffic by bushes, poles, berms or traffic signs, as shown above. Remember that the strength of the medium resides in the fact that most high-traffic roadways are very strictly defined courseways, and that the lines of sight for people driving on them are constant and predictable. The above sign, on the southbound side of Highway 17 between San Jose and Santa Cruz, took about a minute to post, start to finish. It's entirely invisible to southbound traffic and practically unreachable to northbound.