Huy Ong can sum up the far-reaching implications of the planned Southwest Corridor MAX line—both its potential benefits and feared drawbacks—with one question:

“Who is this system being built for?”

As the director of OPAL Environmental Justice Oregon, Ong and his colleagues work to improve public transportation in Portland, particularly for low-income people and people of color. And they have concerns about the region’s newest MAX line.

The plan to build a new light rail line to connect Portland’s city center to Tigard and other Southwest suburbs has been in the works for almost a decade. It’s gained significant steam in the last year, as the Metro Council, TriMet, and the cities of Portland, Tigard, and Tualatin have worked together to form an official proposed route.

That proposed 13-stop MAX route would start at the south end of downtown Portland and follow Southwest Barbur to Tigard, ending at the Bridgeport Village mall. The new line is expected to start operating sometime between 2027 and 2035.

If the plan is executed well, Ong and other transit advocates say it has the potential to give millions of metro area residents quicker and more reliable transportation to home, work, and school. But if the plan doesn’t also include a promise of affordable housing, they argue it could transform much of Southwest Portland into a haven for the rich and push out lower income residents.

Michael Andersen is a senior fellow at the Sightline Institute, a transit and affordable housing think tank. When he imagines the best-case scenario for what the new MAX line could be, he looks to Orenco Station.

Orenco Station is one of the last stops on the MAX Blue line, which connects Gresham to Hillsboro through the Portland city center. Orenco is home to a mixed-use development that includes retail, office spaces, and affordable housing. The station attracts more riders than many of TriMet’s bustling stops that serve more than one MAX line.

“It’s a perfect example of what could be possible in lots of locations, if we made it legal,” said Andersen.

Andersen’s referring to the restrictive zoning rules that have kept multi-use development from popping up along Southwest Barbur, like the fact that large swaths of residential areas surrounding Southwest Barbur are zoned for single-family use. Many of these homes are deemed “naturally occurring affordable housing,” a term used to describe housing that is not officially designated as affordable but remains relatively low-rent because of factors like age, location, and surrounding amenities. (According to Zillow, the average home price in Multnomah Village, the neighborhood just north of the Barbur Transit Center, is about $400,000.)

But if zoning in the Southwest Corridor remains as it is, home prices could skyrocket after the new MAX line opens—and rent for that naturally occurring affordable housing could also jump.

“If we spend the same amount of money, we could have 1,200 below-market homes, each of them with several residents.” —Michael Andersen, the Sightline Institute

“The crucial thing is not what happens even to the existing structures,” Andersen said. “If the only thing we’re allowed to do is replace it one-for-one, then eventually every home there is going to be replaced with a huge single-family home, and that’s a big waste.”

This concern isn’t lost on the agencies involved. Ten percent of the $652.8 million Metro housing bond, passed by voters this month, will be dedicated to acquiring and protecting existing affordable housing across the region. And the City of Portland—the only jurisdiction that could change these zoning rules—has green-lighted a housing plan for the Southwest Corridor that suggests tweaking zoning codes along Southwest Barbur to mitigate the displacement of current residents.

“There is a lot of focus on Barbur, to allow Barbur to grow taller, so that the areas around them in the existing neighborhoods can stay less dense,” said Eryn Kehe, a Metro spokesperson. “Right behind Barbur is where a lot of neighborhoods start, and I think they’ve focused their energy on trying to preserve neighborhoods the way they are.”

Asked if they think it’s feasible that Portland would drastically change its zoning codes along Barbur, OPAL’s Ong and his colleague, Orlando Lopez Bautista, were skeptical.

“It’s something that we definitely want to challenge all the jurisdictions—Portland, Metro, the county—to see what their vision is,” Lopez Bautista said. “We need to continue to build and make Portland a bit more dense.”

And if changes aren’t made to protect the affordability along Southwest Barbur? That’s where Andersen’s “nightmare scenario” comes in: Southwest Portland turning into another Laurelhurst.

The Blue, Red and Green MAX lines all run through the Hollywood/42nd Avenue Transit Center, making it one of the most convenient transit centers in the city. South of this station is the Laurelhurst neighborhood, where the median home price is about $700,000, according to Zillow.

“The fact that you’ve got all these million-dollar houses in walking distance, that’s nice for those individuals,” Andersen said. “But so many more people could be served by allowing [multifamily development].”

Park-and-rides—the free parking lots next to MAX stations intended for commuters—are a key part of Metro’s plan for the new line. The amount and capacity of park-and-rides for the line is still up in the air, but Metro’s recent Draft Environmental Impact Statement indicates their plan could include as many as 4,200 parking spaces—more spaces than TriMet has included on any other MAX line. Considering the City of Portland’s estimate that creating a single parking space costs about $50,000, that could mean as much as $2 million of the $2.8 billion project will be spent on parking alone. TriMet only expects about 15 percent of the route’s frequent users to use those spaces.

“If we spend the same amount of money, we could have 1,200 below-market homes, each of them with several residents,” Andersen said.

Construction on the Southwest Corridor MAX line isn’t expected to begin before 2022, meaning there’s still time to cobble together an affordable housing plan for Southwest Barbur.

Metro’s Kehe is hopeful that’ll happen.

“We want to bring people in to participate in making this a system that works for everybody, and there’s lots of opportunity for that,” she said. “[The plan] is not cooked.”