"If that signaling issue couldn't be resolved prior to the opening date, we were going to put out an order saying 'We can't start,'" said Michelle Cooke, the interim director of the PUC's Consumer Protection and Safety Division.
After the Chatsworth Metrolink crash in 2008, the MTA required the Expo Line designers to upgrade the line's safety mechanisms. The addition of "Automatic Train Protection" cost an extra $5 million and was responsible for some of the project's delay. The system is designed to prevent trains from colliding by automatically slowing them to a stop when they get too close.
The ATP system is especially important at the junction where the Expo Line meets the Blue Line, at Washington Boulevard and Flower Street.
The trains are designed to automatically slow to a halt when they lose contact with the ATP system. Over the last few months, engineers have been dealing with trains that fail to recognize the signal, and come to a halt for no reason.
During a ride for the news media in late March, Art Leahy, the CEO of MTA, said the problem had been fixed earlier that week. But according to Cooke, the issue was still unresolved as recently as last week.
Cooke said the PUC was worried that trains would come to a stop in the middle of an intersection, and that drivers and pedestrians would get frustrated and go around it. They could then be struck by a second train traveling in the opposite direction.
The MTA and the Expo Line Construction Authority worked last week with the L.A. Department of Transportation to adjust the timing of some traffic lights to account for the problem. The issue was fixed to the PUC's satisfaction on Tuesday, Cooke said.
Marc Littman, an MTA spokesman, said that such issues are normal when a train line first starts up.
"We would not open if it wasn't safe," he said.
Littman said MTA will have an "army" of staffers out this weekend, working to make sure the line runs smoothly. In the worst case scenario, however, he said there are buses standing by to ferry passengers to the next stop if a train gets stuck.