Updated 8:20 p.m.

The MBTA may re-examine its fall maintenance workload and schedule after a construction accident extended a planned weekend shutdown into the Monday morning commute.

Service on the heavily used core subway line was back up and running by 2:30 p.m. Monday.

MBTA General Manager Steve Poftak hinted Monday that T officials might adjust how much work they plan to accomplish during a stretch of consecutive weekend closures in the wake of the incident, which pushed thousands of commuters onto shuttle buses and other train lines at peak travel times.

"If that's something we need to adjust, we will adjust it," Poftak said in an interview after an MBTA board meeting. "We're going to learn as we go. Right now, there are no plans to curtail the number of weekends, but we may be changing our expectations around the amount of work that can realistically get done."

The issues arose over the weekend, which was the third of six straight weekends with the Orange Line scheduled to be closed for maintenance. Crews initially faced problems because of "unforeseen site conditions," Poftak said, but that the problem "cascaded" Sunday night.

Two vehicles used to transport tracks and ballast collided between the North Station and Community College stops, Poftak said. One contractor, who had been operating one of the vehicles, was taken to the hospital complaining of chest pains.

Delays spread through the system as the Monday morning commute began. Orange Line passengers were asked to use shuttle buses between Sullivan Square and Haymarket, then to use the Green Line — whose Copley stop is about a quarter-mile from the Orange Line's Back Bay Station — to reach destinations downtown and farther south.

"We regret the inconvenience, not only to our Orange Line riders but to our Green Line riders and to our bus riders," Poftak told reporters Monday. "We had to pull buses off routes so that we could run this level of bus diversion. This is not the service we want to provide."

n August, two months after a Red Line derailment brought heightened scrutiny to the quality of the MBTA's infrastructure, the MBTA unveiled a $27.5 million plan to expand weekend shutdowns on down parts of the Red, Orange and Green lines so that crews could gain access to system and make significant improvements.

Some, such as almost three straight months of no weekend service on the Green Line's D Branch, had already been planned, but the new proposal called for six straight weekends of closures on the heart of the Orange Line and four weekends off for the Red Line through Boston.

Officials said the closures would pose difficulties for riders, but would allow much-needed repair work to take place on a shorter overall timeline than doing repairs only at nighttime.

"If you think about the work window overnight, where it may take two or three hours to mobilize, two or three hours to work, two or three hours to demobilize — if you're doing a diversion over a weekend, that two or three hours of mobilization and two to three hours of demobilization only happens once and then you've got, depending on your timeframe, a 40- to 50-hour window where you can work continuously," Poftak told WGBH in a Facebook Live interview this month. "It makes a big difference."