I certainly don't meant to appear insensitive toward the tragedy of the many motorists who strike kangaroos, wallabies, deer, and elk. I'm sure that these accidents do cause a great deal of personal, physical, financial, and emotional trauma to the drivers and their occupants. However, the animal rights activist in me can't help but point out that it isn't really their fault. We've built giant concrete pathways right through their habitats and now we're racing our big steel cages down them at 100km/h (or 60mph). That isn't really something we can reasonably expect them to understand, never mind modify their behaviour to. It's also worth remembering that practically every kangaroo/wallaby/deer/elk and human motorist collision ends up at least as bad, and usually worse, for the animal in question than for the human.
Anyway, obviously ideally these accidents should be avoided in the first place. I wouldn't presume to be able to solve such a complicated problem, but I would assume that the solutions lie in strictly enforcing greatly reduced speeds for motorists passing through these areas (or else not building roads there in the first place) and/or perhaps the local governments building very good, very extensive fences around their roadways. Granted this probably initially seems impractical given that the most troublesome areas are usually the ones that are the most "in the middle of nowhere", but if building the fence came standard right along with building the highway it would get done. I could also be maintained at the same times that the roads were being maintained. Of course it wouldn't be perfect and would probably still inevitably be broken and useless in some places, but it would probably help.
Anyway, just my thoughts,
-Kevin