| Contextual Infrastructure Planning and Design |
| Minimizing Impacts of Roadways on Animals and
Their Habitats |
| By Carol C. Martsolf, Philadelphia, Pennsylvania 1-215-790-2319,
martsolf@pbworld.com |
| Funding has been made available
recently in the U.S. for wildlife crossings on new and existing roads.
This article focuses on the need for such crossings. Several examples
of their implementation are presented, including special considerations
for different animal species. |
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Many social and environmental issues associated with transportation
planning and design have been given due attention recently, including
sprawl, air pollution, noise impacts, water quality concerns, the
protection of natural resources, enhanced aesthetics, and many others.
These issues, which are not foreign to the transportation community,
are increasingly becoming a part of planning and design discourse.
As population increases and we build more infrastructure to support
it, the impact of human development on the environment increases.
Our infrastructure should be planned and designed to minimize its
impacts so we don't deplete the environment's limited resources.
In addition to realizing the social and environmental impacts our
transportation facilities can have on humans, we are now focusing
more on their impacts on the animals and other creatures that have
to co-exist with these facilities. In addition to the obvious impacts
to animals-water quality and air quality--transportation facilities
may interrupt their natural movement and migration patterns and fragment
the territory that they need for food foraging and other biological
needs. Also, roads directly impact animal populations because millions
of animals are killed every year by vehicles. Conversely, about 200
motorists are killed each year and thousands more injured in animal-vehicle
collisions.
A Closer Look at Three
Critical Impacts
It is important to plan and design highways to minimize impacts to
animals, and to better understand the predominant ways in which roadways
can be a serious threat to wildlife-collisions, habitat fragmentation
and habitat loss. These are complicated issues.
Wildlife-Automobile
Collisions. Many species of animals have long-established migratory,
dispersal, foraging, and mating behavior that can cover an area of
several square miles or more. The introduction of a highway that bisects
their traditional travel paths may not deter them from continuing
their instinctive behavior.
Wide-ranging, large carnivores like wolves, grizzly bears, and mountain
lions are vulnerable because they need to cross many highways for
their needs. Smaller animals like turtles and salamanders are at risk
because they are slow-moving. Several other species, including deer,
moose, raccoons, woodchucks and others, are vulnerable for a combination
of reasons, including limited eyesight, a slow pace, and the fact
that some species' migratory patterns occur at night, when visibility
is greatly reduced.
Habitat Fragmentation. Many animals
do not try to cross new highways, yet roadways still affect them negatively.
Studies have shown that some species of animals will not attempt to
cross even infrequently-used dirt roads or paths. Roadways can fragment
different populations of these species by promoting genetic erosion
due to isolation, inbreeding and the lack of population diversity
needed to sustain the viability of the species. There is a greater
risk of extinction, not by direct population reduction, but by the
lack of genetic diversity.
This "habitat fragmentation" also splits species into small,
fragmented segments that are more vulnerable to population fluctuations
because they have lost their ability to interact and roam. This loss
can cause an imbalance, particularly between predator and prey, and
possibly make them more susceptible to disease. According to Paul
Garrett, an ecologist with the Federal Highway Administration, "Roads
effectively can become very solid barriers to a lot of species of
wildlife."
Habitat Loss. Habitat loss is caused
by many factors, such as residential development, agricultural conversion
and other land development. Roadways cause habitat loss not only because
of the actual area needed to build and support them, but also because
roadways make areas that were previously pristine and remote more
accessible to human populations, causing land conversion and secondary
development.
Actions and Initiatives
to Protect Animals
Roadway construction and human development do not necessarily have
to be commensurate with environmental degradation and species erosion.
Under the Transportation Equity Act for the 21st Century (TEA-21)
in the U.S, Federal Highway Administration (FHWA) funding was made
available for wildlife crossings on new and existing roads. Also,
other funding can be made available by expanding the definition of
"transportation enhancements" to include habitat connectivity
applications. These sources can provide funding for the design and
construction of measures to protect animals, and for including conservation
biology, landscape ecology, and human safety issues into long-range
transportation plans.
More and more, it is being understood that highway planning and design
is an interdisciplinary effort of engineers, environmental professionals,
wildlife biologists and other professionals. Many exemplary projects
and design applications are helping to minimize negative impacts.
Animal Underpasses and Overpasses
Animal underpasses and overpasses are being constructed along species'
natural travel paths and migration patterns to allow movement between
the two sides of a roadway. Several examples of these facilities,
described below, provide a safe means for wildlife to cross the road
without endangering their lives or the lives of motorists.
- State Route 87 in Arizona, a PB project
that received the FHWA Environmental Protection and Enhancements
award in 1998, included many amenities to protect animals because
the new construction was located within the Tonto National Forest.
The area is home to various species of cactus as well as gila
monsters, hawks, frogs, bats, beetles and rattlesnakes. Native
bats pollinate rare cacti in the area and control the insect population.
These bats are so vital to the ecosystem that the concrete box
culverts along the corridor were roughened to encourage bat habitation.
- U.S. 441 in Florida's Paynes Prairie State
Preserve has "ecopassages" that consist of a smooth
concrete walls that stand 1 m (3 feet) tall and have lips at the
top so reptiles cannot climb over them. The walls guide animals
to four conduits, which provide a safe passageway under the roadway
for alligators, frogs, snakes, turtles, mice and lizards, and
larger animals like bobcats and otters.
- Thirty-six culverts were constructed along
a 64-km (40-mile) section of Alligator Alley (I-75) in Florida
at a cost of $13 million. Mile marker 78 (Alligator Alley) is
lined with grass and ferns, and it provides animals a wide view
to the other side. Ecologists working with radio tracking collars
and heat-sensing cameras have verified that panthers and other
animals are using the culverts.
- On S.R. 46 in Lake County, Florida, the underpass
built by the Florida Department of Transportation is a bear-friendly,
dirt-floor box culvert 14 m (47 feet) long, 7 m (24 feet) wide
and 2.5 m (8 feet) high. Research revealed that bears and 12 other
species of animals, including bobcats, gray foxes and whitetail
deer, were using the structure.
The design of animal overpasses and underpasses is relatively new,
and there are some considerations that need to addressed as we learn
more about their use. An understanding of animal behavior is important
to make sure the overpasses or underpasses are designed so the animals
will feel comfortable using them.
For instance, wolves and bears are wary animals. They need time to
discover the underpasses, and then more time to get used to using
them. Some animals are wary of entering dark places where their predators
may be, so some of the underpasses have to be well-lit. Underpasses
for predator and prey must be separated substantially; optimally,
they should be placed along the corridor to protect both. It has also
been speculated that the underpasses and overpasses should not be
in areas where people will use them because some animals may not use
the structures if they detect a human scent. These issues and others
can be investigated to improve the structures as the ones already
built are monitored further.
Conclusion
With the funding provided by TEA-21, transportation professionals
working in collaboration with wildlife and biology professionals can
best design transportation facilities that can have minimal impacts
to the environment and to the animals that live there. Some devices
are already in use to help protect the animals, such as signage, but
studies have shown that underpasses and overpasses combined with fencing
to direct the animals have made a dramatic improvement in protecting
animals. These initiatives are just another step toward making the
environment a better for place for all who live and co-exist within
it. |
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| Carol Martsolf is a design engineer for transportation
projects in the Philadelphia office. She is currently the President
of the Younger Member Forum of the American Society of Civil Engineers,
Philadelphia Section. Carol received the 1999 ASCE Daniel W. Mead
Prize for Younger Members and was awarded the 1999 ASCE-Philadelphia
Young Engineer of the Year award. |
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