An important factor to consider when designing outdoor is does your message communicate effectively within 10 seconds? That's how long your viewer will have an opportunity to see your ad. Remember, if your ad is on a highway, cars are traveling at an average of 55 mph or more. If the ad is cluttered with too much info, the viewer will not get this info gradually over time. Instead they will ignore the ad altogether as too hard to read. Simplicity is key to a billboard's effectiveness. It is generally recommended to use no more than 7 words.