Every two-sided billboard has two distinctly different ad faces to rent -- the right-hand read and the left-hand read. The right-hand read is the side of the sign that is seen on the right-hand side of the street, while the left-hand read is the side that is always seen on the other side of the road, beyond the lane carrying traffic the other direction.
In almost all cases, the right-hand read is considered the more desirable side -- in the old days, billboard companies often built one-sided signs and didn't bother to even put left-hand reads on the structure. With the significant cost of the steel monopole structure, it became imperative that there be two income units, so almost all modern signs have two sides.
Renting the left-hand read is significantly harder than the right-hand read. However, there are three key benefits to the left-hand read that you need to enthusiastically present to your client to make such a sale possible.
The first benefit to the left-hand read is that you can see it for a longer time. Due to the parallax angles of the orientation of the car and the sign, all of the clutter that would block a billboard is visually spread out much farther on the left-hand read -- it goes clear of obstructions must faster. As you approach a right-hand read, all of the business signs and power poles line up in front of it, and you can only see the sign free of clutter when you get fairly close to it. The left-hand read frees itself visually of all of the clutter up to two times farther back.
The second benefit of the left-hand read is that it is the side nearest the driver. If you look at how a driver's eyes are oriented when driving down the road, it is easier for the driver to read the left-hand read than the right-hand read. The right-hand read is easier for the passenger to read. For the driver, the rear-view mirror and passenger side roof pillar obstruct the visibility of the right-hand read. This, obviously, does not include right-hand read situations where there is a curve in the road creating a head-on visibility.
The final benefit of the left-hand read is that they are almost always cheaper than the right-hand read. Although everyone prefers the right-hand read, the question is "just how much is that preference worth"? Assuming that people commute on the same road system every day, and assuming that in today's bumper-to-bumper traffic jams they like to look at new things. They will see your left-hand read about as much as the right-hand. They will also see your ad message many, many times. So maybe the discount on the left-hand read is a pretty good deal.
As soon as you understand the benefits of the left-hand read, you will be able to rent it more aggressively and successfully. Who knows, over time, it may become your favorite side to rent.