What's the most effective way to advertise next to a highway?

To attract the attention of drivers going by at a fast clip on a busy highway, you should have very simple signage.  That means boiling it down to a simple message of no more than about five words (if you have a large enough space), and a single visual.  If you can make that message contain an intriguing benefit, rather than just a name, so much the better.   Avoid fancy fonts or letters in all capitals.  Both are very hard to read and actually slow the reader down.  Not the kind of thing you want when you only have 2-3 seconds in which to grab their attention.  Also, studies show that yellow lettering over a black background is the easiest for the human eye to see.