But what if they all went away?
Here's what I'm thinking. And I don't think it will be some concerted effort of environmentalists that will do it. I think, if it happens, businesses will voluntarily do it because it will make fiscal sense.
Almost everyone I know has some sort of smart phone now. The numbers just keep increasing. It won't be long before everyone has one and is locked in. Cars are even coming with screens built into them. If it is not here yet, soon the screen in your car, based on its location, will pop up ads for all the fast food places and coffee shops at the next exit. Businesses will be able to buy time, say 15 seconds, of display on your screen as you come into town. Click here to get more information. Click here to see the menu. Likewise the same information can pop-up on smart phones. The question then will become opt-out-ability. But, let's face it, you can't opt out of billboards right now. Whoever writes the app will give you just enough free stuff so that it is tolerable for you to allow the ads.
At some point, when the electronic apps are selling enough... getting enough eyeballs, billboards could become redundant. They could become an extra, unnecessary expense. At that point, they may begin to fall apart.
The good news is, we'll be able to see the trees again... if we can pull our noses out of our smartphones long enough to look.
Image from Wikimedia Commons