Strategic capacity assessment of Thailand’s Southern railway corridor for future ASEAN cross-border operations

The Nakhon Pathom-Padang Besar section of Thailand’s Southern Railway Corridor is a key national route and is a major part of the Singapore Kunming Rail Link (SKRL). It supports domestic rail operations and cross-border connectivity with Malaysia. Upgrades, including partial double-tracking and signalling modernization have been implemented to improve operational efficiency. However, mixed-track infrastructure and temporary E-Token train control during the transitional period have restricted corridor capacity. Little empirical research has been conducted during the transitional upgrade of infrastructure and signalling arrangements. This study evaluates the line capacity of the Southern Corridor during the transitional phase using train graph modelling and the UIC 406 compressed timetable method. The effects of infrastructure configuration, signalling systems, traffic growth, and train speeds are investigated through six scenarios across three sections (A to C). The results show that the single-track of the Nakhon Pathom-Chumphon section (Section A), is the main bottleneck with 98.4 percent capacity consumption. Section B from Chumphon-Hat Yai Junction has 95.2 percent and Section C from Hat Yai Junction-Padang Besar has 24.4 percent capacity consumption. In the future, upgrading the whole corridor from Nakhon Pathom-Padang Besar to double-track would reduce capacity consumption to below 40 percent. During the transitional upgrade period, only Section A is double track with E-Token signalling deployment, while Section B and Section C are still single-track without E-Token signalling. During the transitional upgrade, Section A capacity consumption is 41.6–42.6 percent. This is around 5–6 percent higher than in the completion phase because of the longer block sections needed for the E-Token arrangement. Section B has become the new bottleneck with the same 95.2 percent capacity consumption. In the transitional upgrade period there is a 39 percent increase in traffic volume in Section A-B, which results in capacity consumption of 61.1–66.7 percent for Section A and 98.9 percent for Section B, reaching the UIC 406 acceptable limit. Increasing the maximum speed of freight trains from 70 to 100 km/h in the double-track section reduces capacity consumption by approximately 7 percent. This implies that additional upstream trips in Section A from Chumphon to Nakhon Pathom or central Bangkok can be increased. Section C, which is referred as the Hat Yai Junction-Padang Besar cross-border section has no problem with the 24.4 percent capacity consumption with existing train services. Additional regional cross border traffic between Thailand and Malaysia can be promoted even during the transitional upgrade period. The evidence-based insights support infrastructure upgrades and service enhancement prioritization under the double-tracking and transitional operating conditions.