Generating Reduced Emissions by Electrifying New Buses Act or the GREEN Buses Act This bill limits eligibility for certain grants that support projects to reduce emissions of public transportation vehicles. Current law permits the use of the grants for (1) projects related to both low- and zero-emission vehicles, and (2) constructing new and improving existing public transportation facilities to accommodate such vehicles. This bill limits the use of the grants to (1) projects related to no-emission vehicles, and (2) improving existing public transportation facilities. The bill also sets out additional criteria that apply to the grants. For example, the bill specifies the minimum number of buses that must be procured through a grant. Furthermore, at least 10% of grant funds must be distributed to projects that predominately serve low-income communities.