They facilitate air and noise pollution. Road dust covers plants, reducing photosynthesis. Road-cuts disrupt groundwater flow patterns. Road-cuts and road shoulders are avenues for noxious weed invasions. Precipitation evaporates from road pavement instead of percolating into the ground.
Roads provide access for slob hunters, poachers, off-road vehicles, and litterbugs.
In short, in most situations wildness and roads are mutually exclusive. Roadless areas are the bridge to a bigger interconnected system of ecologically viable wildland reserves. The scientific assessment from the Interior Columbia Basin Ecosystem Management Project found that undeveloped, roadless areas are important for providing habitat for native fish and water quality, are economically valuable to society, and are in relatively good ecological condition. Roadless areas are not protected from road building, logging, or other management activities. Roads may have unavoidable effects on streams, no matter how well they are located, designed or maintained.