Effective integration of data across multiple agencies involved in national transportation and infrastructure systems is essential for informed policy-making, strategic planning, and operational efficiency. However, such integration faces substantial challenges, including data silos, interoperability issues, inconsistent standards, and governance complexities. This paper proposes a comprehensive policy-oriented framework designed to enable seamless multi-agency data integration while maintaining data quality, privacy, and security. The framework emphasizes institutional collaboration, standardized data protocols, and governance models that align with national strategic priorities. It incorporates policy levers to incentivize data sharing and outlines technical and organizational mechanisms to support interoperability among heterogeneous systems. By addressing regulatory, technological, and institutional dimensions, the proposed framework facilitates real-time decision-making, enhances predictive analytics capabilities, and supports infrastructure resilience and sustainability. The framework is validated through case analysis and expert consultation, demonstrating its practical applicability in bridging agency-specific gaps and fostering an integrated national transportation and infrastructure data ecosystem.