Some animals make their own roads. Deer in the woods, muskrats in a marsh, and leafcutter ants through a tropical forest all leave their trails. But most natural trails are temporary, disappearing within a few seasons of being made. Human-made roads, in contrast, may last for decades or even centuries, and their impacts on a habitat surpass that of any other animal species. Human highways unquestionably have major environmental impacts on plants, animals, and habitats.
Roads can change the direction of natural water flow, affecting the way wetlands function.
Roads can dissect the landscape so that normal movement patterns of native species that move overland are disrupted. Countless animals are killed on roads by vehicles every day. Certain indirect effects of roads can also be damaging to natural habitats and wildlife. Roads can carry people into remote and pristine regions, which can lead to commercial development, mining, logging, and exploration for oil. None of these activities are intended to have a negative impact on natural systems, but without special attention, all can.