"The doors are what drive our reliability," Hopkins said, noting that if doors don't work, a train often will be delayed, throwing other trains off schedule, too.
Mechanical doors on buses and trolleys are less problematic, he said.
Other transit agencies in the Northeastern United States have had similar problems with door operations and other equipment failures in the cold weather, Hopkins said.
SEPTA maintenance crews have used chemical deicers, heaters, and manual cleaning to try to improve door functions, he said.
Agency officials met Friday with the manufacturers of the doors in the Silverliner V cars to see whether operational changes or retrofits can reduce the failures.
During the assembly of the new cars at a South Philadelphia factory, there were repeated issues with the doors. The 120 Silverliner V cars - about a third of SEPTA's Regional Rail fleet - were made in South Korea by Hyundai Rotem, a subsidiary of automaker Hyundai Motor Group, and assembled in Philadelphia.
SEPTA is paying $330 million, including spare parts and training, for the Silverliner V's. The last of the cars were delivered last year, two years behind schedule, as the work had been delayed by material shortages, design flaws, production problems, labor conflict, and workmanship errors.
Since Tuesday's snowstorm, riders and train crews have complained about door failures, especially on the new cars.
Though some older Silverliner IV cars have also been afflicted with malfunctioning doors, the new cars' sensitive computer-operated doors seem more prone to failure, Hopkins said.
This is the first big winter test for the Silverliner V's, he said, because the last two winters have been relatively mild.
Matthew Mitchell, president of the Delaware Valley Association of Rail Passengers, said, "If you could pick a situation that is going to make things tough for them, this is it."