Rural ACO Improvement Act This bill requires the Centers for Medicare & Medicaid Services (CMS) to exclude certain components from a methodology used under the Medicare Shared Savings Program. The program enables accountable care organizations (ACOs) to receive payments for savings stemming from care coordination and management. Specifically, the bill requires the CMS to exclude an ACO's assigned Medicare fee-for-service beneficiaries from certain regional adjustments to the ACO's benchmark for savings determinations, and to otherwise ensure that an ACO is not in a less favorable financial position due to its share of assigned beneficiaries in the region.