Fozzybear,
Thanks for the link...but they didn't make any solid conclusions on the deer whistles one way or the other. They did mention what DD said above as a warning about a false sense of security.
With a sighting almost every trip, frequent near misses, and about one per year hits lately, we aren't likely to get overly secure.
The deer in our area have seen a steady increase in numbers over the years. It has generally been a good thing, except for the road hazard. Because we have deep, heavy timber that comes right up to the road right-of-way in many places, it can be very difficult to see deer emerging from those places. I hit one last winter during mid-day that just sprinted out of the deep woods and into the side of the truck...a glancing blow.
I hate to kill a deer this way, but even more hate to read about people loosing their lives while trying to avoid collisions with deer. I'll hit the brakes but will not swerve sharply to miss a deer and put the lives of myself and family at risk. I was hoping these whistles might be an answer, but it seems they are not...at least conclusive. Thanks to all for the responses.