Three years after MBTA service problems were exposed by the harsh winter of 2015, the transit authority’s systems are being put to the test again with another week of frigid temperatures and heavy snowfall in the forecast.

Transit officials are advising riders to prepare for potential delays this week as the cold snap continues. In recent days, MBTA users have faced a blend of satisfactory service combined with sometimes lengthy delays and cancellations as the area copes with a string of below-freezing days and riders deal with late arrivals and missed appointments.

A “huge amount of work” is going into attempts to minimize disruptions for passengers, Transportation Secretary Stephanie Pollack said Tuesday.

“If we’re running five or 10 minutes late, that’s way better than 2015, when service was shut down for days and even weeks at a time,” Pollack said on WBUR’s “Radio Boston.” “But because of the cold weather, we just want to make sure our customers plan for that kind of eventuality, because there’s just a big difference, given this temperature, between standing and waiting for your train for five minutes and standing and waiting for your train for 20 minutes.”

Gov. Charlie Baker said extreme cold can be “almost more dangerous and difficult than snow.”

“Rails break, and when rails break, that creates all kinds of issues for riders,” Baker said Tuesday, according to a WHDH broadcast.

There have been eight broken rails on exterior portions of T lines during the recent cold spell, Pollack said, and seven were repaired without service disruptions. Orange Line passengers north of Boston on Friday were rerouted onto shuttle buses after a piece of rail broke on a bridge near Wellington Station in Medford, causing delays.

One major aspect of service south of Boston was knocked offline completely Monday night when the T announced that its ferry from Hingham to Boston would be suspended until further notice after “extreme tides and ice buildup” damaged a dock.

The damage was severe enough to constitute a safety hazard for passengers, according to the T, which advised ferry customers to instead board the Greenbush commuter rail line.

Some rail, subway and bus passengers were greeted Tuesday morning with delays attributed to mechanical issues, signal problems, track conditions and disabled trains or buses. Morning train cancellations were reported on the Fitchburg and Newburyport/Rockport commuter rail lines.

Overall, approximately 84 percent of the morning’s roughly 200 commuter trains were on-time Tuesday, a spokesman for commuter rail operator Keolis told the News Service. Justin Thompson, Keolis’ public relations manager, said the rail company expected to run a “normal level of service” Tuesday evening and that officials are “taking precautions to help ensure this evening’s commute is smooth and comfortable for our passengers.”

Over the past seven days – not including Tuesday – buses were running at an average 75 percent reliability, commuter rail at 88 percent and the subway 85 percent, according to MBTA data.

Keolis is encouraging passengers to dress warmly and check schedules before traveling. Additional crews will be on hand to clear snow from platforms, apply sand and salt and inspect tracks and signals ahead of and during Thursday’s anticipated storm, according to a press release.