food, shelter and mates will experience reduced reproductive and survival rates, which can compromise population viability. In addition to the first three factors, numerous studies have shown that the construction and use of roads is a direct source of habitat fragmentation. As mentioned above, populations surrounded by roads are less likely to receive immigrants from other habitats and as a result, they suffer from a lack of genetic diversity. These small populations are particularly vulnerable to extinction due to demographic, genetic, and environmental stochasticity because they do not contain enough alleles to adapt to new selective pressures such as changes in temperature, habitat, and food availability. The relationship between roads and habitat fragmentation is well documented. One study found that roads contribute more to fragmentation in forest habitats than clear cuts. Another study concluded that road fragmentation of formerly contiguous forest in eastern North America is the primary cause for the decline of forest bird species and has also significantly harmed small mammals, insects, and reptiles in the United States. After years of research, biologists agree that roads and traffic lead to habitat fragmentation, isolation and road kill, all of which combine to significantly compromise the viability of wildlife populations throughout the world. Wildlife-vehicle collisions Wildlife-vehicle collisions have a significant cost for human populations because collisions damage property and injure and kill passengers and drivers. estimated the number of collisions with ungulates in traffic in Europe at 507,000 per year, resulting in 300 people killed, 30,000 injured, and property damage exceeding $1 billion. In parallel, 1.5 million traffic accidents involving deer in the United States cause an estimated $1.1 billion in vehicle damage each year. On a larger scale, research indicates that wildlife-vehicle collisions in the United States result in 29,000 injuries and more than 200 fatalities per year. The conservation issues associated with roads (wildlife mortality and habitat fragmentation) coupled with the substantial human and economic costs resulting from wildlife-vehicle collisions have caused scientists, engineers, and transportation authorities to consider a number of mitigation tools for reducing the conflict between roads and wildlife. Of the currently available options, structures known as wildlife crossings have been the most successful at reducing both habitat fragmentation and wildlife-vehicle collisions caused by roads. Wildlife crossings are structural passages beneath or above roadways that are designed to facilitate safe wildlife movement across roadways. In recent years, conservation biologists and wildlife managers have advocated wildlife