Accessible Transit For All Act of 2020 or the ATFA Act of 2020 This bill directs the Department of Transportation (DOT) to establish a grant program to provide public transportation agencies with technical assistance and funding for infrastructure improvements at transportation access points to facilitate or increase the use of transportation facilities by individuals with limited mobility. An awarded grant may not exceed $5 billion and five years in duration. The federal share of the costs of a project assisted with a grant under the program may not exceed 80%, with specified exceptions for agencies that demonstrate financial hardship. DOT shall prioritize grant applications from agencies for (1) the construction, rehabilitation or modification of transportation access points to facilitate use for persons with limited mobility that meet certain requirements under the Americans with Disabilities Act of 1990; (2) projects located in urbanized areas; and (3) projects located in areas where there is no accessible transportation access point within one mile of such point.