Technological Evolution and Safety Enhancement of Automatic Couplers in Modern Railway Systems: A Systematic Review

The global railway industry is undergoing a significant transformation toward a safer, more efficient, and sustainable transportation system, in which the automatic coupler serves as a vital component ensuring connectivity, safety, and operational reliability of train formations. Despite rapid technological advancements, existing research on automatic couplers remains fragmented, with limited integration between mechanical design, energy efficiency, and safety aspects. This study is aimed at systematically analyzing the technological evolution of automatic couplers in railway systems through a systematic literature review (SLR) approach based on the PRISMA protocol, utilizing literature indexed in Scopus and Web of Science from 2000 to 2025. The collected data were thematically analyzed to identify research trends, coupler classifications, and their contributions to operational efficiency and safety. The findings reveal a clear evolution from conventional mechanical coupling systems toward the digital automatic coupler (DAC), which integrates mechanical, electropneumatic, and digital communication functions. These innovations have proven to enhance efficiency by reducing longitudinal forces, extending fatigue life, and minimizing maintenance costs while simultaneously strengthening safety through energy absorption systems, high-strength materials, and synchronized digital brake control. Scientifically, this study provides a novel contribution by offering a comprehensive mapping of the technological trajectory of automatic couplers and emphasizing the urgency of integrating mechanical and digital design principles to support automation and sustainability in the future of railway systems.