NEPA Agency Process Accountability Act of 2020 This bill revises the environmental review process required under the National Environmental Policy Act of 1969 (NEPA), including by limiting the number of assessment documents required for proposed major federal actions, requiring agencies to reuse certain research or documents in the NEPA process, and allowing agencies to adopt environmental documents prepared by states or third parties as specified under the bill. In addition, the bill requires agencies to only consider alternatives to proposed major federal actions that are technically and economically feasible. Agencies must track and report on specified NEPA data, such as the comprehensive costs of the NEPA process.