From Digital Representation to Cooperative Control: A Review of Smart Highways Enabled by Digital Twins and Vehicle–Road–Cloud Integration

Smart highways increasingly integrate smart cameras, IoT sensors, connected vehicles, edge–cloud computing, and digital twins to enhance traffic management and infrastructure services. However, existing research often emphasises technological capabilities rather than verified operational benefits, leaving gaps in system integration, performance evaluation, and practical deployment. This integrative critical review examines how digital twins and vehicle–road–cloud (VRC) integration can support reliable and coordinated highway operations. Drawing on relevant research, technical standards, and documented deployment programmes, the study proposes a four-plane architecture comprising measurement, interoperable communications, analytics and digital twin, and assured services. It clarifies the interactions among vehicles, roadside edge nodes, and regional cloud platforms, emphasising validated data exchange, predictive analysis, and safety-governed feedback. Applications in incident response, corridor traffic management, and infrastructure maintenance are critically examined in terms of technical capabilities, operational evidence, and deployment constraints. Comparative assessments of the Wyoming and Tampa connected-vehicle pilots and the C-Roads deployment indicate that demonstrated technical feasibility and service availability do not necessarily establish measurable improvements in corridor-level safety, mobility, or environmental performance. To address this gap, the review presents a four-tier evidence hierarchy covering component performance, service effectiveness, corridor outcomes, and lifecycle value, together with a safety-gated deployment framework progressing from reliable data infrastructure to supervised analytics, bounded control, and cross-corridor validation. The findings highlight data quality, model reliability, communication interoperability, cybersecurity, and operational governance as critical challenges. The review concludes that successful smart-highway deployment requires validated virtual–physical feedback, independently assessed operational benefits, and phased implementation under clearly defined safety and institutional constraints.