I live in Montana. I drive deer infested roads all the time. I've been using the air deer whistles for 16 years and I have seen deer turn back from heading into the road too many times to count.
In my opinion, if you live where there is a lot of wildlife along the roads you are nutz not to have them. I'm not saying they will work 100% because stuff just happens. So far they have worked 100% for me.