All four lines of the TTC's rapid transit system were shut down for more than an hour this morning due to a massive communications system failure. Just before 6:30, both the primary and back-up radio systems the TTC uses to communicate with its subway vehicles suffered a server malfunction, Mayor John Tory said. As a result, all four lines were closed, and no buses shuttle buses were deployed.

Station buildings across the network were closed to prevent overcrowding, leaving thousands on the street in the pouring rain. It's not clear at this stage whether storms last night and this morning had anything to do with the system failure. John Tory said there were not enough spare TTC buses to initiate a shuttle service.

All four subway lines were restored shortly after 7:30 a.m. with residual delays across the system. TTC spokesman Brad Ross said riders should expect to wait for their next train while service is being restored.

Tory said there would be an "intensive investigation" into the "highly unusual" failure.

"I think the decision was correct, as frustrating as it was, to close the subway," the mayor told Breakfast Television. "Operating the subway without radios is kind of like trying to operate the airport without radios."

Currently, the TTC uses radio to communicate with its drivers. The system is currently in the process of being replaced.

Chris Bateman is a staff writer at blogTO. Follow him on Twitter at @chrisbateman.

Image: memeyer/Twitter.