Smart highway refers to a system that comprehensively applies new-generation information technologies to achieve digital, networked, and intelligent upgrades of highway infrastructure, thereby significantly enhancing efficiency, safety, and sustainability. Although the importance is increasingly prominent, current studies focus on specific technologies or regional development analyses, lacking a systematic review and comparison of the global evolutionary trajectory of smart highways. By synthesizing the trajectories of representative countries and regions, the evolution of smart highways can be understood as proceeding through several stages, ranging from the early emergence and exploration, to the rise of ITS, and further to stages characterized by cooperative vehicle-infrastructure systems and digital development. The conceptual characteristics and technological connotations of various stages are investigated. The evolutionary process of system architectures across countries is analyzed, through which a development trend is revealed toward a physical hierarchy structured around the cloud-edge-end paradigm and a logical hierarchy centered on sensing-communication-computing-application. On this basis, key enabling technologies are summarized in the domains of sensing, control, safety, and vehicle-infrastructure cooperation. The findings are expected to contribute to a more comprehensive understanding of the concepts, architectures, and technological evolution of smart highways, while providing the references for technical road mapping, standard publishing, and large-scale deployment.