OTTAWA -- Canada’s transportation safety watchdog is investigating wheel cracks on Ottawa’s problem-plagued LRT system.

The Transportation Safety Board issued formal notice on Friday that it’s conducting an investigation after cracks were found on a total of four wheels on three separate Ottawa light rail transit vehicles.

A class 3 occurrence is described as one that “may have significant consequences that attract a high level of public interest,” and when there is public expectation the TSB would investigate.

Since the first wheel crack was discovered Friday morning, trains on the Confederation Line have been running less frequently due to increased inspections.

That means seven trains are being provided each day, rather than the usual complement of 13. Ridership on the system is down because of the COVID-19 pandemic.

In a memo confirming the TSB investigation on Friday afternoon, transportation services general manager John Manconi said "a visual inspection is being performed on every wheel of the entire fleet, prior to each vehicle's entry into service."

This is the latest setback for the $2.1 billion rail line, which has been beset with problems since it launched last fall.

Late last month, the Confederation Line was completely shut down for extended maintenance for a week.