Bridging the Gap: Highways and Wildlife
The mileage of the U.S. highway system numbers in the millions and crosses many types of landscapes—urban and rural—and through many habitats, both human and wildlife. According to the Humane Society of the United States, millions of wild animals are killed on our nation's highways every year. The organization Defenders of Wildlife has found that death by automobile has pushed some rare species—such as the panther and grizzly bear—closer to extinction.
Collisions with wildlife are also a threat to humans. An estimated 200 motorists are killed and thousands more are injured each year in and near auto accidents involving wildlife. The insurance industry estimates that the annual cost for these accidents is $200 million. On average, hitting a deer costs about $2,000 in vehicle repairs.
In addition, development around highways produces a fragmentation of wildlife habitats. This creates increasingly smaller areas in which larger groups of animals are expected to live. These areas do not meet the needs of the animal population, which drives them to attempt highway crossings in order to find food, shelter, and mates.
These factors have led to endeavors to create functional and cost-effective wildlife management practices around highway and road systems. Through the combined efforts of wildlife and highway agencies, as well as local governments and lawmakers, progress is being made in the research, planning, and implementation of measures to aid in the reduction of highway impacts on wildlife.
The introduction of wildlife crossings to highway design has proven to be an effective mitigation measure for highway systems. Wildlife crossing designs include signs, culverts, box culverts, multi-plate arches, open-span bridges, bridge extensions, and wildlife overpasses.
Efforts Abroad
Wildlife Crossing on the 26 Motorway in the Hardt Forest in Germany. photo: Javier Martinez de Castilla, Head of the Environmental Department, Ferrovial Agroman
European efforts have led the way in highway designs that lessen the impact of development on wildlife. The construction of a variety of safeguards, including overpasses, underpasses, and tunnels for both amphibians and small mammals, has had positive results for habitats, wildlife, and drivers. For example, fences and tunnels around and under both major and minor roads in the Netherlands have helped to substantially boost population levels of the endangered European badger. Since the fences were installed, the badgers are using the tunnels every night, as are other small mammals. Due to this success, these badger fence installations are now being considered as additions to any new highway built in the Netherlands.
Some countries are also closing portions of highways to allow seasonal migration to occur. Taiwan, for example, closed one lane of a major highway in spring 2007 to allow more than a million purple milkweed butterflies to pass over 600 yards of motorway to reach their breeding ground in the north of the island.
Closer to home
Here in the U.S., wildlife crossings are helping to slow the decline of some species. In Florida, for example, the panther population had declined to less than 40 animals by the 1980s. After the 1993 construction of wildlife crossings (barrier fencing and box culverts) on I-75 in Eastern Collier County, no panthers have been killed on this stretch of interstate.
Another project to help lessen the decline of animal populations is the Wildlife Bridge in progress at West Vail Pass in Colorado. This bridge will reconnect a significant wildlife habitat in the Rockies that was bisected by Interstate 70. This habitat is of particular importance to the threatened Canadian Lynx. The vegetated bridge, one of the nation’s first, will work in conjunction with the seven underpasses already in place. Wildlife fencing will also be installed to help prevent wildlife from crossing the highway between these installations and help guide them to the new structures.
Many DOTs and communities are also installing wildlife crossing structures to reduce the number of collisions that occur every year. Arizona, for example, recently deployed an electric wildlife crosswalk on SR 260. The crosswalk is meant to reduce collisions by providing drivers with information sent to ITS signage. The project uses infrared cameras and software to detect objects and provides drivers with warning messages on signage that is placed in advance of the crosswalk in both directions.
Working Together
Land Bridge over I-75, Marjorie Cross Florida Greenway Photo by A. Murray Copyright 2001 Univ. Florida
This issue has many different aspects and there is no one perfect answer. Wildlife crossings are just one means to diminish the threat to biodiversity in growing areas of development and make the highways safer for both drivers and wildlife. The efforts of many organizations and disciplines will need to be combined to create comprehensive, feasible solutions. Through the funding of research, development, and implementation of new and effective mitigation measures, science, engineering, communities, and government entities can work together to stop the collision of urban development and natural resources.