The city is looking at opening Edmonton's troubled Metro LRT line in a reduced capacity while problems around the contentious signalling system are hammered out.

Going without the signalling system would reduce the frequency and speed of LRT service. But that is the only way to open the Metro Line to public service as quickly and safely as possible, Transportation Services general manager Dorian Wandzura told reporters Friday.

No timeline was given, but Wandzura said more information would be presented to city council Aug. 17.

While there are no observable safety issues with the system, documents needed for the city to accept certification are missing, he said.

The city requires certification from the system contractor, Thales Rail Signalling Solutions, before it can open the line using the signalling system.

Because Thales failed to provide some "essential" documents, the city has hired a consultant to audit all documentation related to the line's signalling system, Wandzura said.

Rail Safety Consulting will review Thales' documentation and identify the missing documents, he said.

"Rail safety systems are based on testing, certification (and) producing an audit trail that can be followed," Wandzura said. "It's a bit like writing an algebra exam and simply writing your answer at the bottom. You need to show your work for full marks."

A spokeswoman for Thales said the decision to conduct an independent review came as a surprise.

Julie Rolland said the company has provided all necessary documents to the city. She said the city's consultant was at the Thales office in Toronto earlier this month.

"On July 24, 2015, Thales received in-person feedback from the City's consultant at the end of its visit," she said in a written statement. "At this time, no comment was made regarding missing essential documentation. No formal or written feedback regarding the city consultant's visit has been received by Thales so far."

However, a city spokesman refuted those claims. Graeme McElheran said Thales was told a third party was being called in to conduct the review and that Thales has not provided documents the city asked for.

NAIT students said they are disappointed with the news, but resigned to other arrangements.

"We have confirmed that the downtown to NAIT direct Ookspress (bus service) will be running in September for students to use," said students association president Justin Nand in a news release.

The $700-million project is now 15 months behind schedule.

Earlier this month a leaked report listed a series of flaws in the construction of the line, including water pooling on the tracks, loose guard rails, and compromised electrical conduits used in the signalling and communication systems.

The two-year-old report surprised city councillors who characterized the project as a mess, a boondoggle and an embarrassment, though the project and city managers reassured them all the problems in the report have been rectified.

The only problem remaining with the project is the signalling system, they said, something the contractor disputes.