In the 10 days since a Red Line train with 60 aboard derailed in Dorchester, MBTA officials have been hesitant to offer an exact estimate of when full service would be restored, citing the complexities of repairing signal infrastructure wiped out by the careening six-car set.

Now, it is clear the timeline is months, not days or weeks, meaning more headaches on a route that runs from Braintree through Quincy, Dorchester, Boston, Somerville and Cambridge and averages 240,000 weekday trips.

On the first day of summer, MBTA General Manager Steve Poftak announced Friday that delays of 10 to 20 minutes on the Red Line would persist "at least through Labor Day." That means slower service for people trying to get to work or home during a summer that will feature fare hikes effective July 1.

"We understand how disruptive this has been for riders," Poftak said at a press conference. "Our priority is on improving service, doing it as quickly as we can but doing it as safely as we can."

Some progress has been made since the June 11 derailment just outside the JFK/UMass station — commuters no longer need to change trains to access the Braintree line, for example — but because bungalows housing the signal system sustained considerable damage, MBTA crews must manually direct traffic and will run fewer cars.

"In those bungalows are systems that essentially control train speed, train spacing and even ultimately throwing switches between the Ashmont and Braintree branches that allow us to operate the Red Line every day," Deputy General Manager Jeff Gonneville said at Friday's press conference.

A standard rush hour will see 13 to 14 trains running on the Red Line every hour, but for the summer, the system will only be able to accommodate 10. Delays and crowding are likely to come with that.

The key challenge, Poftak said, is that the equipment damaged in some cases dates back to the 1970s. He and Gonneville spoke to reporters in front of a table with examples of the affected technology, pointing out the damage and the specialty parts needed for restoration.

Crews are using whatever pieces they can for now and are in the process of finding additional repair materials, but that is not an easy task when the parts are several decades old.

"We are working to restore the full level of service using some of the existing equipment and any equipment that we can secure," Poftak said. "It is a very complicated process. Some of this equipment is obviously not the type of thing that you buy off the rack."

The derailment also pushed up the MBTA's timeline on plans to modernize signalling in the area. A project was already underway to replace analog signals near Columbia Junction with digital ones by 2021, but Poftak said officials are now working with the contractor to complete that work by 2020.

There is some chance for service to improve over the course of the summer, ahead of the Labor Day deadline outlined Friday, officials said. As signal circuits come back online, the MBTA may be able to reduce the almost 50 workers manually directing trains and run them more quickly.

"We are working every day to decrease the amount of manual work that's being done, and if we are able to make sufficient progress, that number will decrease," Poftak said. "But I think to allow the riding public to plan, right now, we foresee this current level of service persisting at least through Labor Day."

After a week and a half, investigators have ruled out track infrastructure, operator error and foul play but still have not determined a cause for the derailment, which was the fifth this calendar year and the 24th on an MBTA passenger train since the start of 2015.

They are looking closely at the 50-year-old train itself and its wheel truck installed in 2014. But that process, Gonneville said, is also challenging because it is not yet clear which parts were damaged as a result of the derailment that sent the train skidding more than 1,800 feet and which may have broken down prior to — and therefore caused — the incident.

"We are at the point now where there is a detailed metallurgical analysis or a detailed analysis that needs to be done to forensically identify what came first, so what was the cause and what was the effect," he said.

Asked by a reporter if budgetary changes contributed to the derailment, Gonneville answered, "Absolutely not."

Authorities investigated similar components on all of the 68 other Type 1 cars currently in passenger service on the Red Line in the wake of the derailment and found no issues, they said. Poftak stressed several times on Friday that he believes the system remains safe to use.

Despite anticipating delays for most of the summer and significant outcry from riders and elected officials, the MBTA has no plans to pause a set of fare increases set to take effect July 1. The changes vary by ticket type, but a single ride on the Red Line will soon increase 15 cents and a monthly subway pass will go up $5.50.

"I think the requests to delay the fare increases are just an expression of frustration in the wake of the derailment," Transportation Secretary Stephanie Pollack told reporters Monday. "I am totally sympathetic to that level of frustration. I just think the fare increase is the wrong target for that frustration."

Asked about the topic after Friday's press conference, a T spokesman said Monday's statements still stand.