Protruding screws might have caused cracks to form on the wheel hubs of multiple Ottawa light-rail trains earlier this year, according to preliminary results from an investigation by Canada’s transportation watchdog.
The Transportation Safety Board (TSB) launched an investigation in July after four cracked wheels were discovered across three trains in Ottawa’s LRT system.
The TSB said in an update on Tuesday that its probe has now revealed a total of eight cracked wheels.
A preliminary analysis from the TSB and train maker Alstom has pointed to protruding jacking screws on the rear surface of the wheel hubs as a possible contributing factor.
These screws are used to separate the axle hub from the wheel hub, according to the TSB report.
A change in processes saw these wheels shipped to Alstom from wheelmaker Lucchini with the jacking screws already attached, the TSB said. Normally, the wheels would’ve been shipped with plastic or silicone plugs in the jacking screw holes to protect the material, and the screws would only be installed when a wheel separation was necessary.
The TSB suggested this change was done without any checks in place to ensure the screws weren’t interfering with the adjacent axle hub.
In some cases where breaks were identified, the report identified corresponding cracks to the placement of jacking screws on the wheels. In others, even where cracks weren’t observed, indentations on the axle hub corresponded to the screws protruding from the wheel hubs.
Wheels equipped with these jacking screws continue to be checked for cracks at the end of each day of service on the LRT line, the TSB said.
City staff had already said in September that the misaligned screws were a likely cause of the cracks and that Rideau Transit Group had committed to replace the wheels.
But the transportation watchdog recommends the expedited removal and replacement of the Lucchini wheels with any protruding jacking screws — 116 out of a total 185 wheels, according to the report.
The TSB investigation is ongoing and could find other contributing factors to the cracks.
“It is likely that other factors also contributed to the development of the cracks observed in the resilient wheel hubs,” the report read.