Roads affect biodiversity in many ways, and this chapter explains these impacts using the Mean Species Abundance (MSA) metric. When roads are built, they remove natural habitat and divide landscapes into smaller, isolated patches. They also create disturbance zones where noise, pollution, and human activity reduce the abundance of mammals and birds. The GLOBIO model quantifies how both habitat fragmentation and disturbance reduce MSA for warmblooded vertebrates. These impacts decrease with distance from the road, creating a clear gradient of biodiversity loss. For each country, the model calculates how much MSA is lost per kilometer of road by linking observed species responses with road density. The result is an impact factor that expresses biodiversity loss in terms of MSAloss per km of road, rather than the PDF metric used in other impact categories. These factors can be further converted to impacts per tonkilometer or personkilometer when assessing road transport.