The entire Sound Transit Light Rail system shut down at peak rush hour during Wednesday's record-breaking temperatures. Sound Transit says heat did play a role – but it is not responsible for the full system shutdown.

The trouble started at Othello station with a part called a turnbuckle, which loosens or tightens a wire. “It expanded due to the heat and the wire sagged and set off the problems with the trains at Othello,” said John Gallagher of Sound Transit. “It was just that one piece of equipment. For whatever reason the heat affected that single piece.”

But then a much bigger problem occurred. A defective switch cut power to the entire light rail system. That fault even included communications, meaning passengers in trains and on platforms saw and heard no information about the outage. Sound Transit did get the word out on Twitter.

Gallagher said a group of switches has been disabled until they can be reprogrammed.

The outage was “a very bad concurrence of events for which we are really sorry,” he said. And he said the heat was not the reason why the switch triggered the shutdown.

In South Seattle, a section of 4th Avenue S. buckled as temperatures hit the 90s. Seattle’s Transportation Department says that section was old and didn't have expansion joints to give it room to expand in the heat. That section of road was not seen as a high priority for repair.