Transportation is currently the biggest contributor to US GHG emissions, accounting for 27% of emissions. Transportation decarbonization is typically viewed as a three legged stool, consisting of improved energy efficiency, fuel decarbonization and reducing vehicle miles traveled (VMT). To reduce VMT, we need to understand how people are traveling now, how they can make individual changes to travel more efficiently, and most importantly, how we should design our cities so that the easiest option is also the most energy efficient. In this talk, we discuss the challenges involved in creating an individual transportation carbon meter (NREL OpenPATH) that can help achieve all these goals. We then describe how NREL OpenPATH has been used to evaluate e-bike programs for low-income workers in Colorado and downtown workers in Durham. We conclude by outlining the continuing challenges and our plans to address them.