State transportation officials on Tuesday defended their winter preparations on MBTA subway and commuter rail lines after track failures caused a train to derail and resulted in service interruptions on the Red Line as temperatures dropped to their lowest since last February.

Transportation Secretary Stephanie Pollack blamed the track breakdowns on the cold but said a full investigation has been launched to determine why a section of track on the Haverhill commuter line shattered as a train carrying a conductor and an engineer passed by early Tuesday.

Pollack said the track problems there and along the Red Line at Savin Hill and Central Square stations do not signal a failure of the state’s efforts to improve service after last year’s record-breaking snowfall pushed the subway and commuter rail networks to the brink.

“I don’t want people to think because we had these unfortunate disruptions today that it means that the winter preparations are not going to result in a better commute,’’ Pollack said at a news conference.

“I want people to understand that being prepared for winter does not mean there will be no service disruption whatsoever,’’ she said.

The problems coincided with two developments that rile commuters: the discussion of fare hikes to fix the Massachusetts Bay Transportation Authority’s operating budget problems and the first bitter cold of 2016.

The temperature in Boston plunged to a low of 8 degrees Tuesday morning for the first time since Feb. 24, said Kevin Cadima, a meteorologist at the National Weather Service in Taunton. The mercury inched its way up to the mid-20s later in the day, he said.

Last winter’s chronic transit problems prompted Governor Charlie Baker to establish an $83.7 million “winter resiliency plan’’ to fix infrastructure, upgrade snow removal and deicing equipment, and improve transit operations during severe weather.

Baker, the MBTA, and other state transportation officials cited these efforts at a series of public announcements as winter approached.

Despite these preparations, commuter rail operator Keolis had the first train derailment the state has seen in years on its hands by 3:30 a.m. Tuesday.

That’s when 30 feet of track failed on the Haverhill Line near the Andover-Lawrence border, causing three coach cars to go off the rails as the train headed north at 56 miles per hour, officials said. No passengers were aboard the train and no one was injured, Keolis said.

Franck Dubourdieu, Keolis’s deputy general manager, said the conductor and engineer “did a great job to stop the train,’’ which was traveling below the speed limit of 60 miles per hour.

“It was not I would say a major derailment, but it was a derailment,’’ Dubourdieu said.

The derailment caused significant delays and 10 trains were canceled during the morning commute, Keolis said in a statement prepared for its customers.

Other routes west and north of Boston also experienced problems, because the track failure stranded four trains at a facility on the Haverhill Line, said Keolis spokeswoman Leslie Aun.

Shaun Connor, a software engineer from Salem, said he waited for about 20 minutes in the cold after an 8:18 a.m. train on the Newburyport/Rockport Line was canceled without advance notice.

“It was because of the disruption on the Haverhill Line, which shouldn’t have affected me but seemed to have affected everyone,’’ Connor said. “It’s very frustrating, and this is the very beginning of the winter.’’

Service on the Haverhill Line was restored Tuesday afternoon, though the commuter rail reported delays on its Twitter account during the evening commute.

The Federal Railroad Administration said it is investigating. Transit and State Police investigators were also summoned to the scene, though they said there was no evidence of foul play.

Officials said the Haverhill Line was inspected Dec. 19 with technology that uses sound waves to detect flaws in the track.

Routine inspections are done twice weekly, and a third inspection was scheduled for Tuesday because of the cold, Dubourdieu said.

Pollack described the track failures on the Red Line as more typical breaks that can happen in cold weather.

The line was closed for repairs during part of the morning commute between the JFK/UMass and Ashmont stations, and shuttle bus service was put in place. A permanent fix was expected before the Wednesday morning commute, Pollack said.

Shuttle bus service was not needed while the MBTA repaired the track at Central Square, she said.

Prior to winter, the MBTA said it upgraded heaters and replaced third rails along parts of the Red Line’s Braintree branch, where many outages were caused last year by power problems. The Ashmont branch of the line, where Savin Hill Station is located, is due for upgrades next year.

Pollack highlighted ways the readiness plans paid off Tuesday. No signals froze, and Orange Line trains ran smoothly after being stored in tunnels overnight, she said.

That was cold comfort to Jamie Drenel as he tried to get to South Station after the MBTA implemented bus service on the Red Line.

“Wasn’t the T just in the news about how they were going to fix everything?’’ he asked.

John R. Ellement contributed. Laura Crimaldi can be reached at laura.crimaldi@globe.com. Follow her on Twitter @lauracrimaldi.