As of last September, 16 states and Puerto Rico approved legislation requiring reductions in greenhouse emissions. The White House also set ambitious goals of cutting emissions by at least 50% below 2005 levels in 2030. They aim to achieve a net-zero economy by 2050. Contributing to 29% of all greenhouse gas emissions in the U.S., the transportation sector is now the top producer and accounts for a growing portion each year. More than half of these emissions (57%) come from personal vehicles such as cars, SUVs, and light-duty trucks. Progress in cutting those emissions has been slow, let alone efforts to measure and track them.