The GREEN Streets Act requires the Department of Transportation to establish new performance standards for transportation projects that prioritize reducing greenhouse gas emissions and decreasing per capita vehicle miles traveled. States and metropolitan areas must incorporate these climate and emissions reduction goals into their transportation planning, and projects seeking federal funding to add highway capacity must demonstrate that they are more cost-effective than alternatives like public transit or active transportation improvements. If states fail to meet their greenhouse gas reduction targets, they face financial penalties requiring them to spend at least 33 percent of certain federal highway funds on transit expansion, active transportation, and land use projects that support the goals. The bill also establishes national transit accessibility standards to measure how well public transportation serves communities, with larger metropolitan areas required to set and report on performance targets within one year of the standards being established.