Toll Credit Marketplace Act of 2020 This bill directs the Department of Transportation (DOT) to establish and implement a toll credit exchange pilot program to identify the extent of the demand to purchase toll credits, identify the cash price of toll credits through bilateral transactions between states, analyze the impact of the purchase or sale of toll credits on transportation expenditures, test the feasibility of expanding the pilot program to allow all states to participate on a permanent basis, and identify any other repercussions of the toll credit exchange. In carrying out the pilot program, DOT must provide that an originating state may transfer or sell to a recipient state a credit not previously used by the originating state. DOT must also make available a public website on which originating states must post the amount of toll credits that are available for sale or transfer to a recipient state. DOT may terminate the pilot program or the participation of any state in the pilot program if the program is not serving a public benefit or it is not cost effective.