Roads have significant negative ecological impacts on both terrestrial and aquatic ecosystems. They cause mortality from construction and vehicle collisions, alter animal behavior, modify the physical and chemical environment, spread exotic species, and increase human use of areas. Road construction kills sessile and slow-moving organisms, damages adjacent habitats, and alters soil conditions. Vehicle collisions affect many species, particularly vertebrates and invertebrates, with mitigation efforts only partially successful. Roads change animal behavior by altering home ranges, movement, reproductive success, escape responses, and physiological states. They also change soil density, temperature, water content, light levels, dust, surface waters, runoff patterns, and sedimentation, while adding heavy metals, salts, organic molecules, ozone, and nutrients to roadside environments. Roads promote the spread of exotic species by altering habitats and stressing native species. They also increase hunting, fishing, and landscape modifications. Roads are highly correlated with changes in species composition, population sizes, and hydrologic and geomorphic processes in aquatic and riparian systems. More experimental research is needed to complement post-biotic correlative studies. Conservation efforts should focus on avoiding new road construction in roadless or sparsely roaded areas and removing or restoring existing roads to benefit both terrestrial and aquatic biota. Roads have complex effects on ecosystems, including habitat fragmentation, changes in species distribution, and altered ecological processes. They contribute to soil compaction, changes in water temperature and flow, and the spread of pollutants. Roads also facilitate the spread of exotic species and increase human activity in natural areas. The ecological effects of roads are multifaceted and can have long-term consequences for biodiversity and ecosystem health. Conservation strategies must consider the full range of ecological impacts of roads to ensure the protection of natural habitats and species.Roads have significant negative ecological impacts on both terrestrial and aquatic ecosystems. They cause mortality from construction and vehicle collisions, alter animal behavior, modify the physical and chemical environment, spread exotic species, and increase human use of areas. Road construction kills sessile and slow-moving organisms, damages adjacent habitats, and alters soil conditions. Vehicle collisions affect many species, particularly vertebrates and invertebrates, with mitigation efforts only partially successful. Roads change animal behavior by altering home ranges, movement, reproductive success, escape responses, and physiological states. They also change soil density, temperature, water content, light levels, dust, surface waters, runoff patterns, and sedimentation, while adding heavy metals, salts, organic molecules, ozone, and nutrients to roadside environments. Roads promote the spread of exotic species by altering habitats and stressing native species. They also increase hunting, fishing, and landscape modifications. Roads are highly correlated with changes in species composition, population sizes, and hydrologic and geomorphic processes in aquatic and riparian systems. More experimental research is needed to complement post-biotic correlative studies. Conservation efforts should focus on avoiding new road construction in roadless or sparsely roaded areas and removing or restoring existing roads to benefit both terrestrial and aquatic biota. Roads have complex effects on ecosystems, including habitat fragmentation, changes in species distribution, and altered ecological processes. They contribute to soil compaction, changes in water temperature and flow, and the spread of pollutants. Roads also facilitate the spread of exotic species and increase human activity in natural areas. The ecological effects of roads are multifaceted and can have long-term consequences for biodiversity and ecosystem health. Conservation strategies must consider the full range of ecological impacts of roads to ensure the protection of natural habitats and species.