Wildlife crossings are structures that allow animals to cross human-made barriers safely. Wildlife crossings are a practice in habitat conservation, allowing connections or reconnections between habitats, combating habitat fragmentation. They also assist in avoiding collisions between vehicles and animals, which in addition to killing or injuring wildlife may cause injury to humans and property damage.
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 impacts . Scientists estimate that the system of roads in the United States impacts 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. There are four identified ways that roads and traffic detrimentally impact 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.
The benefits derived from constructing wildlife crossings to extend wildlife migration corridors over and under major roads appear to outweigh the costs of construction and maintenance. One study estimates that adding wildlife crossings to a road project is a 7-8% increase in the total cost of the project. Theoretically, the monetary costs associated with constructing and maintaining wildlife crossings in ecologically important areas are trumped by the benefits associated with protecting wildlife populations, reducing property damage to vehicles, and saving the lives of drivers and passengers by reducing the number of collisions caused by wildlife.