Authorities have identified multiple factors contributing to the recent wheel malfunction on Bangkok’s Yellow Line monorail, prompting a series of corrective actions. One key issue under investigation is heat generated by wheel bearings, which may have caused component misalignment. Officials are expediting safety improvements, including the installation of new wheels and enhanced monitoring systems.
The investigation follows an incident earlier this year, when a support wheel detached from a Yellow Line train and fell onto a moving taxi. This event spurred the Mass Rapid Transit Authority of Thailand (MRTA), together with the concessionaire Eastern Bangkok Monorail Co. Ltd. (EBM) and manufacturer Alstom, to determine the root causes and introduce preventive measures.
Alstom’s analysis pointed to friction-related heat build-up inside the wheel bearings and hub, which may have contributed to material expansion and part displacement. In response, Alstom is installing electronic temperature sensors on the guide wheels’ end caps. These sensors connect to the Train Management System (TMS) and will alert operators if temperatures exceed 60 degrees Celsius. Any overheating will trigger an immediate stop and inspection to prevent further incidents.
Additionally, six bolts are being added to secure the guide wheel covers, further reducing the risk of detachment. Alstom has assured officials that these modifications will prevent future wheel malfunctions.
New wheel sets have already arrived from China, with installations underway on two trains—one on the Yellow Line and one on the Pink Line. Testing will begin immediately and run for three months, targeting completion in mid-January 2025. If no issues arise, a fleet-wide replacement of 3,456 wheels across 72 trains on both lines will commence in February 2025, with final installations expected to take six to nine months.
The inspection visit to Alstom’s manufacturing facility in Wuhu, Anhui Province, China, was led by Saroj Taosuwan, Deputy Governor of MRTA, alongside other executives and media representatives. Alstom produces trains for Thailand’s Yellow, Pink, and Gold monorail lines, all of which are currently in service.
