Roads have long been considered the enemy of the environment, creating (literal) avenues for deforestation and development. Now, it seems, they are also to blame for another major environmental woe: invasive species. According to a pair of recent studies conducted at the University of California at Davis, new roads are one of the quickest ways to introduce nonnative species to an area, at a tremendous cost to local flora and fauna. The studies found that invasive species are more likely to be found near roads, and that they spread further with every improvement to roadways, such as grading or paving. Not only does vehicle traffic provide a way for nonnative species to hitchhike into a new area; the roads themselves concentrate runoff, creating a welcoming environment for unwanted species. Nonnative species are considered one of the greatest threats to forests and rangelands in the U.S., invading 1.7 million acres every year.