Habitat fragmentation occurs when human-made barriers such as roads, railroads, canals, electric power lines, and pipelines penetrate and divide wildlife habitat . Of these, roads have the most widespread and detrimental effects . Scientists estimate that the system of roads in the United States affects the ecology of at least one-fifth of the land area of the country . For many years ecologists and conservationists have documented the adverse relationship between roads and wildlife. identify four ways that roads and traffic detrimentally affect wildlife populations: (1) they decrease habitat amount and quality, (2) they increase mortality due to wildlife-vehicle collisions (road kill), (3) they prevent access to resources on the other side of the road, and (4) they subdivide wildlife populations into smaller and more vulnerable sub-populations (fragmentation). Habitat fragmentation can lead to extinction or extirpation if a population's gene pool is restricted enough.