Use of Transportation Network Companies (TNCs) such as Uber and Lyft has grown rapidly in cities across the United States. TNCs often provide a cheaper and more flexible travel option than traditional taxi services, and could improve transportation sustainability if they facilitated more pooled travel and public transit use. However, TNCs’ growth has been linked to increased congestion and emissions. Cities and states have begun regulating TNCs, imposing taxes that are assessed per ride at a flat or percentage rate. Researchers at the University of California, Davis assessed 21 state and local TNC taxes across the United States and developed a method of comparing per-ride and percentage taxes. The researchers then assessed the likelihood of these taxes encouraging more sustainable travel. This policy brief summarizes the findings from that research and provides policy implications.