Reliable data exchange between vehicles and road-side units (RSUs) is critical for intelligent transportation systems, yet communication is often disrupted by low signal strength, intermittent connectivity, and missing acknowledgments. This paper proposes a deterministic, UAV-assisted architecture for fault-tolerant V2I communication using LoRa and IEEE 802.11 backhaul links. In the proposed system, UAVs are triggered when RSUs detect degraded RSSI or ACK loss, thereby providing a redundant relay path to maintain session continuity. All logic is implemented on off-the-shelf embedded hardware without reliance on cloud or simulation platforms. Experimental results from real hardware deployments demonstrate a 14% improvement in message delivery ratio, steady latency of approximately 34 ms, and enhanced SNR performance in low-coverage areas. The architecture is lightweight, interpretable, and immediately deployable for real-world ITS applications.