The MBTA has released video of the June 11 Red Line derailment that officials say will continue to cause delays through most of the summer on the same day that T officials said service on a stretch of track will return to normal two weeks earlier than expected.

After being instructed by the secretary of state’s office Wednesday to respond to a News Service public records request for video of the incident, on Friday, the MBTA provided about six minutes of footage depicting the incident at the JFK/UMass station from two different angles. Sparks are visible for several seconds as the 50-year-old train approaches the station from the north before the third car bucks, prompting additional sparking and smoke.

MBTA officials said that the derailment destroyed one signal bungalow next to the tracks that houses signal equipment and damaged two others. Because of that damage, crews have been manually directing train traffic, creating delays across a transit system that serves hundreds of thousands of riders daily.

The MBTA initially forecast that 10- to 20-minute delays would persist through at least Labor Day because of the damage, but earlier on Friday the agency announced that service would return to normal for a portion of the Red Line between Broadway and JFK/UMass by Aug. 15.

“We thank our customers for their patience while the work continues and regret the frustrations caused by these delays on the Red Line,” MBTA General Manager Steve Poftak said in the press release. “We will continue repair efforts around the clock until we get back to full service along the entire line.”

The three signal structures damaged have been repaired and a fourth one was built. As a result of the work, officials said delays on most trips will be reduced by about five minutes. Still, in stretches of the Red Line that still do not have signal infrastructure restored, crews must manually direct trains when it is safe to advance from station to station, an arduous process that creates delays.

While the stretch from Broadway to JFK/UMass has a new target date, the MBTA said only that “efforts continue to focus” on stretches south of JFK on both the Braintree and Ashmont lines.

MBTA officials still have not announced what caused the derailment, though they ruled out foul play, operator error, and track infrastructure. Investigators believe the train car itself — first introduced into service 50 years ago — or its wheel truck, which was installed in 2014, are likely responsible, and they are conducting metallurgic tests to determine which components failed as a result of the crash and which may have sparked the incident.

The impacts to service have prompted widespread outrage. Boston Mayor Marty Walsh slammed the T as “not currently a functional service” for much of the city in a Wednesday letter to state transportation officials, and Gov. Charlie Baker proposed more frequent service disruptions to speed up long-planned improvements to the core subway system. He also is seeking $50 million in one-time funding to allow the MBTA to bring on additional engineers, inspectors, consultants, and shuttle bus drivers.