The Toronto Transit Commission is defending its handling of a massive service disruption that shut down part of a major transit artery for much of Thursday evening and left thousands of passengers scurrying to find another way to their destinations.

“Safety comes before service,” the commission said in a news release Friday. “The TTC appreciates the frustration these situations can cause, but it will not compromise public or employee safety whenever fire or smoke is detected.”

The problems started at around 4:30 p.m. when smoke was reported on an empty train at High Park Station. That led to a closure between Keele and Islington stations.

Just as that problem was fixed, a communications cable malfunctioned at Runnymede Station, shutting down proper radio communication on part of the line.

Ultimately service was suspended between Keele and Jane for the rest of the day from around 6 p.m.

The shutdown left many customers scurrying to try and find an alternate way of getting to their destinations.

The TTC dispatched shuttle buses and customers were allowed to board GO Train or UP Express service for the price of a TTC fare.

“The root cause of these fires is under investigation,” the TTC said in its release. “The TTC believes, however, that the problem began with a faulty power cable on the underside of a westbound train.”

Service returned to normal Friday morning.