This week's cold snap has caused at least seven rails, which are made of steel, to crack, said LIRR spokesman Salvatore Arena.
By about 8:15 p.m., trains were on schedule or close to schedule, the rail road said.
Arena said the rails are inspected several times a year but cracks and other problems may develop between inspections.
"These rails are designed to function in all kinds of weather," he said. "If the rails are at a point at which they're worn or whatever, there's always the potential for them to fail in the most extreme weather conditions. There's no rail that's totally foolproof."
Trains on several LIRR branches were also delayed Wednesday morning as a result of signal trouble and broken rail conditions believed to be related to the cold weather, the commuter rail said.
Arena said switches often stop moving in extreme cold. They have heaters attached to them, he said, but they're turned on only in certain conditions.
"It's strictly to melt snow and ice," he said. "Apparently they can't run the heater just to keep the switch warm, so to speak, because the thing will burn."