Billboards are the most distracting driving issue (Radius Images|Getty Images )

In the study, researchers at the University of Alberta asked 30 adults to hop into a driving simulator and react to different types of billboards. The boards featured both positive and negative words like "joy" or "stress," as well as target words the drivers were told to look out for, such as "cat" and "lion." If a driver saw a target word, he was supposed to press a button.
(Find out what else you're doing wrong in the garage--and how to upgrade your ride--with our list of The 100 Best Car Tips for Men.)

The results: When billboards featured negative words, the drivers tended to slow down and veer from their lanes, according to the study. The drivers were also slower to spot the target words, which proves the negative language was distracting, says study author Michelle Chan, a Ph.D. student at Alberta. On the other hand, positive words caused drivers to push the pedal to the metal after they'd passed the billboard.
Chan's explanation: Research has shown your emotions affect your attention and decision making. Negative language is more emotionally charged, so it absorbs more of your focus, she says. Meanwhile, the arousing effect of positive emotion actually broadens your focus and energizes you, which could explain the increase in speed. (Click here to learn how to save your life by combatting negative feelings.)

And it's not just words, Chan says. Negative or positive images are likely to have similar effects. Ironically, those frightening billboards showing car wrecks and warning about the dangers of drinking or texting
while driving may actually distract you into an accident, the research suggests.

How can you protect yourself? You're already halfway there. Just knowing that billboards cause distraction can help drivers keep their minds (and eyes) on the road, Chan says. Billboards are especially dangerous in urban areas and on busy roadways, and Chan says she hopes policymakers will enforce stronger regulations regarding where ads can be placed. In the meantime, lowering your visor to block elevated ads could also help, the study suggests.
(For more great ways to keep your mind in tip-top shape, check out 27 Ways to Power Up Your Brain.)