The Safety Funding Parity Adjustment Act of 2025 introduces a new process for the Secretary of Transportation to make adjustments to federal highway safety funding. This legislation specifically targets funding distributed under Section 402 (State and Community Highway Safety Grants) and Section 405 (National Priority Safety Programs) of title 23, United States Code. The primary goal is to ensure a specific proportional relationship in the growth of these two funding streams. Before distributing funds each fiscal year, the Secretary must determine if there is an increase in either Section 402 or Section 405 funding compared to the prior year. If both funding streams increase, an adjustment is triggered unless the percentage increase in Section 402 funding is already at least four times the percentage increase in Section 405 funding. Should this ratio not be met, the Secretary is mandated to reduce Section 405 funding and transfer the amount to Section 402 funding until the four-to-one ratio is achieved. The bill also addresses scenarios where only Section 405 funding increases while Section 402 funding decreases from the prior year. In such cases, Section 405 funds are proportionately reduced and transferred to Section 402 funding, either fully or partially, to bring Section 402 funding up to or beyond its prior year level, maintaining the 4:1 ratio. No adjustments are made if only Section 402 funding increases, or if neither funding stream increases, and this Act is set to take effect on October 1, 2026 .