The State Railway of Thailand (SRT) has completed an evaluation of its diesel-electric locomotive procurement programme, concluding that the 50 QSY mainline locomotives (CRRC CDA5B1) introduced since 2022 are meeting operational and service objectives for both passenger and freight transport.
The review focused on operational performance, service reliability and utilisation of the locomotives, which were acquired to replace ageing General Electric traction dating back to the 1960s.
All 50 QSY locomotives, supplied by CRRC Qishuyan, are now in service across Thailand’s metre-gauge network. The locomotives are designed for mixed-traffic operation, featuring a Co-Co wheel arrangement, 16-tonne axle load and a maximum speed of 120 km/h. With a power output of around 2,400 kW and AC traction equipment, they are used on long-distance passenger services as well as freight trains.
According to the evaluation findings presented by SRT, the introduction of the QSY fleet has supported more stable train operations and higher transport volumes. Passenger traffic in 2023 reached 27.8 million journeys, exceeding the railway’s internal planning assumptions. Passenger satisfaction surveys conducted in 2025 also reported high ratings from users of commercial passenger services and freight operators, with punctuality and journey time among the highest-scoring criteria.
From an operational standpoint, the evaluation highlighted improved hauling capacity and reduced service disruptions compared with the withdrawn fleet. SRT noted that the locomotives allow for longer passenger formations and heavier freight trains within existing infrastructure constraints.
