Figure 3
The diagram displays clusters of keywords related to railroad transportation research. The largest cluster includes railroad transportation and railroads, with key strengths of 143 and 137 respectively. Other prominent keywords include digital transformation, Industry 4.0, logistics, freight transportation, information management, sustainability, IoT, AI, and supply chain. The clusters represent four major themes: value-chain-oriented research, technological foundation of intelligent railway systems, operational and risk-management dimensions, and sustainable railway development. All values are approximated.Co-occurrence keyword analysis using all keywords. Source: Authors’ own work