Dr. Yang, I would suggest searching US government archives, either Interior or Transportation, maybe even EPA. A few years ago, I stumbled upon a report by the U.S. Department of Transportation on the impacts of roadways to wildlife. I don't have the exact reference for that report , but a recent search produced the following:
http://www.tfhrc.gov/pubrds/05may/01.htm
Best wishes,
LGF
