Any attempt to cut back on car accidents is valiant. So if Iowa has to put Taylor Swift on their signs in an effort to wake up zoned out drivers, I'm all for it. However, and this could be my pessimism talking, it seems like Taylor Swift and Pokemon aren't enough to rouse drivers from their trance. I have a few suggestions, take them or leave them.
Personalized road signs with texts from your ex would catch the eye of even the drowsiest driver. "I've completely moved on and found love somewhere else with a person who is superior in every measurable capacity, -Your Ex," would be like caffeine straight to the heart. Sure, you may be crying, and the tears may make it difficult to see the road, but at least you're awake!
Another option is something along the lines of, "Keep watching these signs to find out the exact time, date, and manner of your death." The signs can build up to vague, ominous warnings, like "Your death will be unnatural," or, "Beware chihuahuas." The mortal fear and paranoia is enough to keep a driver alert for hours.
Of course, you could always go with the classic ScantilyCladJeffGoldblum.jpg, though now that I think about it, it would probably just drive people mad with lust and they'd immediately crash as Jeff Goldblum's bare chest consumes their thoughts.