While it is true that the Internet is the place folks do research before they leave on vacation, once they pull out of the driveway, billboards are the way to reach new customers.
The average person spends twenty hours a week in their car! So we are exposed to a lot of advertising but you will only see any given billboard for about three-seconds. Because of this, your message must be short and to the point. A long address and phone number simply will not get read, let alone written down.
Billboards can be very effective when several are purchased. However, they can also be quite expensive in high-traffic tourism areas.