It's officially game over for the TTC's Line 3 Scarborough RT, as officials confirm that service will never resume on the shuttered line following a derailment in July.

Line 3 was initially set to close for good in November, though a July 24 derailment near Ellesmere Station forced the TTC to halt service on the line to conduct an investigation, raising doubts the RT would ever run again.

The TTC confirmed those doubts on Thursday, stating that "the decision has been made to permanently close the line and begin to implement elements of the replacement plan."

The transit agency says that though "a comprehensive review, that includes the participation of industry-leading consultants, is still underway," the length of time required to complete this review does not fit within the line's previously-announced closure timeline.

Bus service was already increased following what was intended to be a temporary closure for the derailment investigation, and the TTC has now committed to improving shuttle service until full dedicated busways come online later this year.

"We recognize the urgency in having this plan ready to go," said TTC CEO Rick Leary. "With the support of our Board and City Council, we will have more pieces of our replacement plan ready to go sooner than planned."

Since Tuesday, TTC crews have been working alongside the City of Toronto Transportation Services department to implement temporary bus-only lanes, road markings, and signage, with the aim of implementation this coming weekend on Saturday, August 26.

A full bus replacement for the entire 6.4 kilometre SRT is still planned to take effect on November 19, running frequent express shuttle service between Scarborough Centre and Kennedy stations southbound via Midland Avenue and northbound via Kennedy Road.

"It is essential to provide safe, reliable transit along this route, and that's what the City and TTC staff are doing," said Mayor Olivia Chow.

"The people of Scarborough deserve better. They need reliable and convenient transit while we wait for the Scarborough subway to open. The sooner we can have transit priority and a dedicated busway in place, the better it will be for the tens of thousands of people who normally rely on Line 3."