"As traffic grows beyond 3,000 vehicles a day, crossing a road becomes extremely difficult. The 13 miles of Interstate 90 here, where grizzly bears would most likely cross, has 8,000 to 10,000 vehicles a day, and so is impermeable much of the time. And it is not just bears - wolves, wolverine and a host of other species roam here.
In recent years scientists have come to understand the marked changes brought by the roads that crisscross the landscape.
Some experts believe that habitat fragmentation, the slicing and dicing of large landscapes into small pieces with roads, homes and other development, is the biggest of all environmental problems. 'By far,' said Dr. Michael Soulé, a retired biologist and founder of the Society for Conservation Biology. 'It's bigger than climate change. While the serious effects from climate change are 30 years away, there's nothing left to save then if we don't deal with fragmentation. And the spearhead of fragmentation are roads.'
Fragmentation cuts off wildlife from critical habitat, including food, security or others of their species for reproduction and genetic diversity. Eventually they disappear."