As the first brand-new Orange Line cars in decades rolled into service Wednesday, public officials expressed hope that the key step toward revamping the system would mark the start of more tangible improvements across a system where riders have grown accustomed to service problems.

It has been a challenging summer for the transit network, with Red Line service entering its third month of delays and riders protesting fare hikes. But the new Orange Line cars, the first in a two-year process to replace and expand the entire fleet with trains that break down less and run faster, are officially here after a "long wait," showcasing what the system may look like in the future.

"There's a ton of work that's been done," said Gov. Charlie Baker during a press conference to launch the new train at the MBTA's Wellington Station. "There is far more left to do. This is a very important day with respect to turning the corner and finally getting some of these trains into service."

Just after 11 a.m., with MBTA General Manager Steve Poftak and Transportation Secretary Stephanie Pollack on board — Baker did not ride — the six-car train embarked on its maiden passenger voyage, accepting commuters from Wellington down to the line's endpoint at Forest Hills.

The new cars, manufactured by Chinese-owned firm CRRC MA and assembled in Springfield, are equipped with a range of features, including wider doors, automatic passenger counters and digital trip information displays. Gone are the fabric seat covers found on many of the trains in service today, replaced by all-plastic versions.

Although MBTA officials did not publicly announce their plans to do so, they took the new train set out of passenger service Wednesday afternoon to analyze its performance.

"The plan was to let it get three round-trips under its belt, and then bring it back in to allow the vehicle engineering team to process data from on board systems and analyze performance metrics," MBTA spokesman Joe Pesaturo told the News Service in an email. "This approach is common when introducing brand new rolling stock to a heavy rail system. The train will be back in service tomorrow."

Asked when the train will begin running a full day's service without a capped number of trips, Pesaturo said, "That will be determined by the vehicle engineering team."

The vehicles are the first new ones to enter Orange Line passenger service since the existing fleet was introduced between 1979 and 1981, a stretch of time, Pesaturo noted, that saw former Pope John Paul II visit Boston and Rosie Ruiz have her Boston Marathon title stripped for not running the entire course.

Wednesday's launch was just the first step: another six-car set sat in the garage during the press conference and is scheduled to begin running in September, and more will go online every few months until the entire fleet is replaced by the end of 2022.

While Baker said riders should expect to feel appreciable impacts in about six months once more trains arrive, the most significant effects will come once the entire project, which also includes track updates and signal replacements, wraps up.

The new fleet will be 32 cars larger than the current one, expanding rider capacity by about 40 percent. Pollack said the T will at first take its oldest cars out of service as new trains arrive, aiming to bolster reliability before expanding frequency and capacity.

By the end of the project, officials said, the Orange Line will run with four-and-a-half minute gaps between trains at rush hour compared to the existing six-minute headways, reducing travel times.

"Customers are going to start seeing these trains more," Poftak said. "They're going to provide a more reliable and more comfortable commute for our passengers."

Officials said they are confident about the safety of the new vehicles, which have a lifespan of about 30 years, despite several derailments on other train lines in recent months. A June 11 Red Line derailmentinflicted significant damage on signal infrastructure, and T officials say normal service will not resume until October.

One woman boarding at Wellington loudly observed that she had never before seen riders excited to step onto an Orange Line train.

"We changed pretty much everything except the color — they're still orange," Pollack said. "They're going to give our passengers a more comfortable ride, a more reliable ride. We're going to get folks where they're going."

Work is also underway to replace the entire Red Line fleet with 252 new cars, though that work is expected to be done by 2023. Together, the projects will cost nearly $2 billion and will add about 85,000 seats to the MBTA's core rail system.

Buildup to Wednesday's launch, though, had some challenges.

After awarding the manufacturing contract in 2014, MBTA officials expected the first ones to launch into passenger service in January. Delays in designing and testing a necessary new signal system pushed the target date to the spring, and in the spring the T again delayed the arrival until summer.

Officials said Wednesday they do not expect those issues to recur as the rollout continues.

"Part of that process when you put a new supply chain in place, especially one that's as big and complicated as this one, is you learn things and have a chance to fix elements of that process and steps along the way so that you don't have the hiccups you might have had the first time," Baker said.

Rep. Shawn Dooley, a Norfolk Republican, criticized the MBTA's work with CRRC, writing in a Wednesday release that the MBTA is "tone deaf" for highlighting the partnership with a Chinese company "while the free world watches in horror as Chinese troops are massing at the border of Hong Kong."

"Celebrating the debut of new Orange Line trains that have arrived late, amidst bipartisan security concerns in Washington DC, all in an attempt to deflect attention from all the T’s other failings speaks volumes," Dooley wrote. "The Commonwealth shouldn’t be doing any business with China, let alone work that invests in our state’s critical infrastructure. Yet here they are - ignoring human rights violations of an anti-democratic regime solely so we can say we got a 'deal' on these cars?"

The MBTA did not respond directly to Dooley's concerns Wednesday, pointing only to Poftak's comments about "tangible signs of progress toward building a better MBTA."