UAV-Based Methodologies for Bridge Inspection: Technological Capabilities, Challenges, and Future Directions

The paper provides a systematic review of the literature on unmanned aerial vehicle (UAV) and unmanned aircraft system (UAS) technologies used for civil bridge inspection, based on a methodology that has been informed by the PRISMA framework for conducting systematic reviews, and follows the steps of that methodology to assemble and analyse a corpus of 54 peer-reviewed studies and technical reports (2019–2026). The review is on the performance of aerospace systems, autonomous flight architectures and integration of airspace. Research papers were systematically retrieved using Scopus, Web of Science and Google Scholar, and were categorised into six synthesis areas: pre-flight operational frameworks, autonomous path planning and optimisation, surface damage detection and photogrammetric reconstruction, structural health monitoring and vibration analysis, Internet of Drones (IoD) communication architecture, and regulatory developments. It reviews the development of consumer-grade multi-rotor platforms to high-performance UAS configurations with payloads of LiDAR, thermal, near-infrared and Laser Doppler Vibrometer, and considers propulsion-energy tradeoffs and payload-endurance constraints for mission planning. The Technology Readiness Level (TRL) is used to evaluate the autonomous flight capabilities. Multi-UAV swarm systems are now at TRL4-5 and sub-pixel bridge displacement measurement from a moving UAS has been field-demonstrated. Deep learning architectures significantly outperform manual defect detection, and suffer from domain-shift vulnerability and lack of edge-compute benchmarking. The landmark regulatory developments in the FAA BVLOS NPRM (Part 108, 2025) and EU U-Space are provided, and an international comparative analysis of the US, EU, China, Japan, South Korea and ICAO frameworks is provided. The key gaps found are: lack of fail-safe and autonomy certification systems; insufficient field testing of AI models on a variety of bridge types; and IoD cybersecurity architectures that have yet to be resolved. Seven directions of priority research are suggested. This review offers a technology and regulation roadmap for operating UAVs to inspect bridges, with a TRL map to guide the use of this technology by aerospace engineers, UAS system designers, and infrastructure practitioners.