The Scarborough RT derailed this past summer after bolts holding down power rails came loose, TTC CEO Rick Leary says.

Leary confirmed the finding to CTV News Toronto Tuesday morning.

“We know that ultimately there are some bolts that came loose, holding down the power rail,” Leary said.

The July 24 derailment sent five people to hospital with minor injuries and ended the life of the troubled line several months early.

“I think when you've heard me speak before about the infrastructure, you know, it (the Scarborough RT) was 38 years old, the design life was 25,” Leary said. “We've talked a lot in the past about state of good repair and needing funding, and unfortunately we've closed it and shut it down and we're running a bus service right now.”

Reacting to the finding, TTC board member Coun. Josh Matlow told CTV News Toronto the derailment was caused by “rusty bolts and political dysfunction” and said the city was lucky that nobody died.

“The derailment happened because too many politicians put their own political interests before getting better transit built for Scarborough years ago,” Matlow said. “In fact, if they had stuck with the Transit City plan, an LRT would have been there back in 2015. And now we're waiting another decade for a subway to be built. Scarborough residents were not only left on the bus for the next decade, but were left with a faulty RT that derailed and could have killed somebody.”

Scarborough RT derailment

The ageing line had a design life of 25 years, but had been in service for 38 years, its lifespan extended several times as debate continued back-and-forth at city hall over how to build transit in Scarborough.

A three-stop subway extension is now being constructed, but won’t be ready before 2030.

Meanwhile, the city has set up dedicated bus lanes on regular roads to replace the RT service. Mayor Olivia Chow has said she wants to see the city build a dedicated busway in the path of the old RT, but the project is not yet funded.

Riders officially bid farewell to the aged line with a goodbye party on Saturday.

- With files from CTV News Toronto Reporter Natalie Johnson