I purchased a billboard a few months ago with a 17,000 per day traffic count. So far, it's costing me $250/month (which isn't bad for the exposure) but I can only track 2 calls to it. Both calls were people calling to lambast me on my choice of marketing. We are in the insurance restoration biz and insurance claims are commonly referred to as 'acts of God'. After some heated debate we chose the slogan 'When God takes a break, We go to work for you' with pics of tornados, fires, you get the drift. You can imagine the jist of the two calls. Bad choice for me. Will use that particular money for internet next year. I am finding it doesn't work that well in our business....at least around here.
Here's a market secret for you and some help on understanding marketing, how and when and why it's effective and when it isn't.
There are two types of marketing, direct and indirect or better known as advertising for an immediate response and branding. When you put an ad in the yellow pages for instance under lets say for instance drain cleaning you are putting yourself in a place that people who have a need for your service are going to actually go to and seek out a solution. When you place a billboard on the road telling people you do drain cleaing it's more of a branding thing.
In the first medium nobody but somebody who needs a drain cleaned will open those pages up and look at them, but those people who do go there will have a need.
In the 2nd medium everybody driving past seeing your message is not driving past your billboard in search of a drain cleaner. When they do need a drain cleaned they aren't going to go driving around the city in search of somebody advertising on a bill board and then go - ah, there he is! and then call you.
If you have other advertising going on all the time, then the bill board is a branding component, reinforcing your existance and keeping you in front of people's minds as when they do have a problem, they will call you cause they know who you are already. But if you aren't already out there creating a brand and keeping your name at the top of the list of who to call in people's minds when they need your service, you're probably wasting your money on something like a bill board.