Regional Infrastructure Accelerator Act of 2017 This bill authorizes the Department of the Treasury to establish a regional infrastructure accelerator (RIA) program to provide initial and subsequent grants to RIAs to facilitate investment in, and long-term financing of, economically viable covered infrastructure projects. An "RIA" is defined as a multi-jurisdictional organization dedicated to providing technical assistance, financing options, and resources for covered infrastructure projects within the represented jurisdictions. A "covered infrastructure project" is defined as a project sponsored by a state, local, or regional public entity that involves the construction, consolidation, alteration, or repair of rail, bus, or public transportation facilities or equipment, highway facilities (including bridges and tunnels), airports, port or marine facilities and equipment, pipelines, inland waterways, intermodal facilities and equipment, water treatment and solid waste disposal facilities, storm water management systems, dams and levees, and facilities or equipment for energy transmission, distribution, or storage. From applications received, Treasury shall select five RIAs from geographically diverse regions to receive initial grants. An RIA shall use such a grant to: assess regional approaches for advancing innovative investment in covered infrastructure projects; develop strategies for transparency in the analysis of such projects to ensure protection of the public interest, for the bundling of smaller scale and rural projects into larger covered infrastructure projects to facilitate transactions and investments, and for reducing transaction costs associated with investments in such projects; facilitate the creation of a catalog of covered infrastructure projects available for investment; and analyze and apply project procurement methods for covered infrastructure projects. Treasury shall review final reports submitted by RIAs and select four of them to receive subsequent grants. A selected RIA shall use such subsequent grant to make subgrants to public entities for costs associated with a covered infrastructure project.