Ice accumulating on the overhead power lines knocked out the Central Light Rail Line yesterday.
It was the first time freezing rain has forced the closing of the entire 22.5-mile-long system for a full day, and the third time bad weather has disrupted service in less than a month.
Service is unlikely to be restored until temperatures rise above the freezing mark, Mass Transit Administration officials said last night.
Passengers have not been stranded by the shutdown, but they have been delayed. A fleet of 24 MTA buses has taken the place of light rail trains, shuttling riders among light rail stations on a schedule as much as 50 percent longer than usual.
The buses yesterday handled fewer than half the 18,617 passengers the system normally carries each day.
The disruption has cast doubts on the dependability of a $364.4 million system that is supposed to lure drivers off the road.
"It's extremely frustrating," said MTA Administrator John A. Agro Jr. "We need to seek out a long-term solution. We haven't found any so far."
When sleet and freezing rain began falling Tuesday night, service was not immediately affected. But despite all-night efforts to keep the lines clear, MTA officials chose not to reopen light rail yesterday morning.
They feared that trains might become stranded as ice interfered with the electrical contacts between the cars and the overhead cables.
"We just couldn't sustain service without facing the possibility of a disruption," Mr. Agro said.
In an ice-related incident Jan. 17, 42 passengers were stranded on one train for more than six hours.
Similar weather closed the system the evening of Jan. 17 and the next morning. Light rail's southern segment was shut down for a week beginning Jan. 19, when ice and cold caused a mile-long section of the overhead wires at Middle Branch to collapse.
The disruptions were the worst in the two-year history of the system and left officials scrambling.
Using a diesel locomotive on loan from Baltimore's Metro, workers created a three-car "ice train" to keep the lines clear Tuesday night.
They borrowed a technique from Philadelphia's mass transit system. Plastic shields installed on the train's pantographs -- the devices on top of each car that make contact with the wires -- were used to scrape ice from the lines.
Workers also linked the cars' pantographs together so that if one of the three made contact with the overhead wires, all would be powered.