Maine Medical Center’s planned $512 million expansion would have a major impact on traffic and parking, and has the potential to alter the fabric of an increasingly popular residential area on Portland’s peninsula.

One of the biggest changes would be moving the hospital’s main entrance to Congress Street and away from Bramhall Street, reducing traffic in the West End and Western Promenade neighborhoods. The expansion, which is expected to be completed by 2022, also could revitalize an area of the city that has been slower than other areas to grow commercially.

But that doesn’t mean the hospital’s plans will go unchallenged.

“They will need to make a strong case for all of their decisions,” said Ian Jacob, president of the West End Neighborhood Association. “This has the potential to be contentious.”

Early criticism seems to be focused on the inclusion of a 13-story parking garage overlooking Gilman Street. That structure would be considerably taller than any other building in the area, further fueling a citywide discussion of how high Portland should build.

“It’s going to be a rather big gorilla,” said Emma Holder with the Parkside Neighborhood Association. “It seems like we’re looking into the past. I don’t think jamming a whole bunch more cars into a small area is going to be helpful.”

The Maine Medical Center campus sits at the crossroads of four different neighborhoods on the west side of the peninsula. Mayor Ethan Strimling said that dynamic likely will mean not everyone is going to be happy with the project.

“But anytime someone invests ($512 million) in the city, that gets my attention,” he said. “We have to be careful and make sure that the process is inclusive and Maine Medical Center has done a good job so far of bringing people in early.” Anne Pringle, president of the Western Promenade Neighborhood Association, also praised the hospital for being proactive in talking to stakeholders. She said that didn’t happen in 2009, when the hospital completed a major project that included a new emergency department, birthing center and neonatal intensive care unit.

Pringle was most pleased about the possibility that the hospital’s main entrance will be relocated to Congress Street. She said the current entrance, at Bramhall and Brackett streets, creates problems for the neighborhood.

But Pringle had concerns, too. She said the increase in parking worries her because it feeds the idea that cars are essential and discourages public transportation. She also worried that Maine Med’s growing footprint could change the fabric of a sought-after residential neighborhood.

“The hospital owns or has acquired a lot of properties in and around its main building,” she said. “I’d like to see them divest some of that property. It could be really valuable.”

Jacob questioned what the hospital will do with its large surface parking lot on Vaughn Street.

“Certainly, that space could be used more effectively,” he said.

City Councilor Spencer Thibodeau, who represents the area that includes the hospital and surrounding neighborhood, said Wednesday that what he’s heard so far has been largely positive.

“I think the movement of the entrance (to Congress Street) is a real game changer for that neighborhood,” he said, adding that the concerns over the parking garage are not insurmountable.

City Councilor Jon Hinck, who lives about three blocks from the hospital, said he understands the medical rationale driving the hospital’s expansion plans.

“I think the challenge is in trying to make sure that the premier hospital in the city functions at the highest level possible, but not at a cost to city neighborhoods,” he said.

Hinck and Strimling both said that the expansion could be beneficial to some businesses in the area, including restaurants.

“If I’m visiting someone there, as I have in the past, and there is downtime, I would go look for something other than hospital food,” Hinck said.

Strimling said the project could be an opportunity to “freshen up the area.”

The scope of the project proposed by Maine Med could ultimately change as the process goes on. The neighborhood associations said they haven’t yet had a chance to meet with their own members to hear their concerns. Holder plans to challenge the hospital on its stated need for more parking, although she knows that likely won’t be met with open arms.

Pringle and others wondered whether Maine Med could locate some of its hospital services elsewhere, such as its campus location in Scarborough, rather than increase its presence in Portland.

“There is no question the hospital is a major part of the city and I’m hopeful they are going to keep everyone involved in the process,” Pringle said.