Marine Highway Promotion Act This bill directs the Maritime Administration (MARAD) to establish a United States Marine Highway Program to designate marine highway routes as extensions of the surface transportation system and provide grants and enter into contacts or agreements for marine highway services. In awarding grants or entering into contracts and agreements, MARAD must give preference to marine highway services that present the most financially viable transportation services and require the lowest percentage federal share of the costs. MARAD may also develop strategies to encourage the use of marine highway transportation for the transportation of passengers and cargo.