Forty percent of the Bay Area’s greenhouse gas emissions (GHGs)—nearly 42 million metric tons a year—come from our cars, trucks, buses, trains, ships and planes. While the Bay Area has begun a serious discussion on ways to reduce transportation GHGs (primarily carbon dioxide, or CO2), we need better information to help us understand which strategies will yield the most cost-effective results. In addition, we must develop a clearer understanding of the important roles that each stakeholder—regional agencies, local governments, businesses, community groups and residents—must play if we are to significantly reduce our transportation “carbon footprint.” The scale of the task ahead is daunting. The chart on page 5 shows the reductions that must be made (both in total and per-capita emissions) for California to reach its climate goals for 2020 and 2050. Since California’s population is expected to grow significantly in this time period, we must strategically focus on transportation strategies that will make a major impact on emissions.The goal of this guide is to spark discussion and generate new ideas in the Bay Area transportation community.