COULD LEAD TO ENVIRONMENTALLY FRIENDLY HIGHWAYS
by Whit Gibbons
April 14, 2003
Last week on Alligator Alley, I saw ecological progress. Alligator Alley
is the nearly straight extension of I-75 connecting Naples, Florida,
with Ft. Lauderdale. In the 1970s and 1980s, before Alligator Alley
was part of the interstate system, roadkills were common, and I saw
many dead snakes, raccoons, turtles, and even alligators.
Now, stopping to check interesting roadkills would be both illegal and
dangerous. But that was immaterial on this last trip, because I saw
no dead animals for almost fifty miles. One reason for this was that
I was traveling at midday when crows and buzzards would have already
picked the highway clean of small snakes or frogs killed the previous
night. But another reason for the lack of larger animals is that Alligator
Alley has 36 culverts, called "panther crossings," that allow
endangered Florida panthers, as well as other wildlife, to travel beneath
the highway instead of across the deadly surface. A 10-foot-high chain-link
fence paralleling the road on each side runs from culvert to culvert.
If a nonflying animal that is too big to get through the mesh of the
fence wants to get to the other side, the culverts are the only way
Under-the-road crossings, or ecopassages, for wildlife are positive
ecological steps that counter the proven negative environmental impacts
of highways. Millions of animals are killed annually on North American
highways, which fragment the habitat into compartments that may be too
small for some species, which then try to cross the road in search of
more suitable habitat. Over the past few years, wildlife have benefited
from hundreds of successfully constructed ecopassages, including those
originally designed for spotted salamanders in Connecticut, toads in
England, and desert tortoises in California.
A situation at Lake Jackson near Tallahassee, Florida, serves as a dramatic
example of the effectiveness of using barriers to redirect the travel
pattern of animals to avoid highway mortality. Matthew Aresco of Florida
State University constructed a guide fence to lead turtles and other
animals to a culvert beneath a highway that bisects the lake. Prior
to the fence's construction, highway deaths of more than 9,000 individual
animals comprising more than 50 different species were documented over
a 3-year period on a half mile of highway. By making the local community
aware that an average of more than 50 animals die each week on the highway,
Aresco has inspired action. The Lake Jackson Ecopassage Alliance comprises
a group of environmentally concerned citizens intent on developing a
permanent ecopassage to connect the two parts of the lake.
A permanent ecopassage has already been constructed along the two miles
where Highway 441 crosses Payne's Prairie, a large wetland south of
Gainesville, Florida. Concrete guide walls prevent or at least discourage
animals from entering the highway from the road shoulder, and culverts
beneath the road give animals the option of moving safely from one side
of the wetland to another. The number of road-killed animals has unquestionably
numbered in the millions since the highway was built in the 1920s, and
a study conducted by Ken Dodd and Lora Smith through the University
of Florida confirmed that mortality remained high in the late 1990s.
They identified and counted roadkills on the Payne's Prairie highway
three days each week for a year and documented that more than 17 animals
were killed each day and night. During the year of the study, they recorded
29 dead alligators on the highway.
Highways, which in one sense are ecopassages for humans, can be highly
disruptive to wildlife populations. When a highway bisects wildlife
corridors, historical migration routes can be cut off. For example,
adult amphibians living in a terrestrial habitat must be able to reach
wetland breeding sites that may be located several hundred yards away.
Guide fences and underpasses to protect wildlife from the human-created
threat of a highway are simple solutions to a major environmental problem.
Road-kill impact assessments should be required before any new highway
is built and conducted for many established roads as well. Ecopassages
should then be constructed in ecologically appropriate sections. Doing
so will make highways safer for wildlife--and where Florida panthers
and large alligators live, safer for drivers.
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