I would have changed it to something more crude. "ZOMBIES AHEAD" while cute to a certain degree, just doesn't keep the "freshness" long enough. I think a better one would have been, "UGLIES AHEAD", since it has an intrinsic ambiguity that leaves drivers confused as to not only what an "ugly" is, but why they need to be informed of it. Why would they need to change their driving habits? Is the "Ugly" stuck in the road? Did it tip over a tanker? Maybe it's a reference to "ugly" weather ahead? Who knows!
unfortunately, this is likely to cause more nervousness on the parts of drivers watching out for these supposed "Uglies" which is likely to cause more crashes...
Other nominees included "GRANDMA AHEAD", "SING A SONG", and the ubiquitous "SHUT UP".