Starting this summer, the Green Line is going to look a little different.

The first of 30 new Green Line cars has arrived in Newton for testing, a major step in the process of expanding Massachusetts Bay Transportation Authority service north beyond what will be a relocated Lechmere Station, where it currently ends, to Medford. The new cars will be introduced into the system starting in July, even though the new extension won’t open for several more years.

MBTA Director of Communications Joe Pesaturo said that the new cars feature a number of improvements relative to their predecessors. The new cars can hold up to 10 percent more passengers, and the interior has been redesigned to provide more space for wheelchairs and strollers, according to Pesaturo.

According to slides provided by the MBTA, the new cars will feature sliding doors, new electronic message boards, automatic stop announcements, new lighting and better systems, such as better brakes, which will improve reliability.

Overall, Pesaturo said he thinks the new cars will positively impact T riders.

“I think people will be impressed when they see these cars,” he said. “They are the most modern light rail vehicle that you’ll find in the country right now.”

While the Medford extension was previously delayed for a few years due to financial concerns, Pesaturo said the new cars were ordered in 2014 to provide service beyond Lechmere and are already in the process of being built.

Annissa Essaibi George, a Boston city councilor at-large, said the Green Line extension is important because the City wants as many people riding the T as possible.

“It helps get people to and from work in a timely manner,” Essaibi George said. “It’s also better for our environment [and] certainly better for our roads. It relieves a lot of congestion.”

Essaibi George also said it’s important to have train cars riders can count on.

“We certainly want to make sure that we have cars that are going to perform for the residents and the riders of the Green Line,” she said.

Peter Furth, a professor of civil engineering at Northeastern University, said while the extension to Medford isn’t open yet, having more trains in the meantime will be beneficial.

“For two years, we’ll have about 30 more cars than we need, so that means it’ll be easier to take … time breaking them in,” Furth said. “If they are working fine, then the MBTA’s looking forward to being able to take some other cars out of service so they can work on them.”

A notable feature of the new cars is that the doors will slide open rather than fold open as they do on the trains currently in service. Pesaturo said these new doors will require less maintenance and be more reliable.

“If you’re a regular Green Line rider, you’ll notice that from time to time the Green Line doors have issues — that will be eliminated with these new doors,” Pestauro said. “It also makes it easier for people in mobility devices to enter or exit a train.”

Elliott Evers, 25, of Kenmore, said he is glad the MBTA is getting new trains, and that the sliding doors will be an important change.

“I’m not going to get stuck in the door ever again it looks like,” Evers said.

Michelle Parkos, 25, takes the Green Line every day. She said the sliding doors are an improvement, especially for people who board in wheelchairs.

“I think it’s great to help improve the speed of the system and will help a lot of people get on the train,” the Brighton resident said.

Furth said the MBTA has a history of problems with different manufacturers for the Green Line cars, from the United States to Japan to Italy. The new “Type 9” trains are being manufactured by a Spanish company, he said, though its design doesn’t deviate much from previous Green Line cars.

Wendy Ballard, 34, lives in South Boston and takes the Green Line into Back Bay. She said the design of the new cars looks more accessible and up to modern code.

“Generally I think the whole idea of them increasing capacity is going to be huge, especially [since] they’re extending the train out to Medford,” Ballard said. “That’s going to increase capacity completely, so they need to add more trains.”