With prices starting at nearly $1.5 million, the townhouses being built just inside the Capital Beltway in Montgomery County promise “modern luxury” with private elevators, designer kitchens and rooftop terraces. Among the neighborhood attractions, the developer notes, is a future light-rail Purple Line station “just steps away.”

At first glance, the Brownstones at Chevy Chase Lake seem to bolster claims of Purple Line opponents who argue that the planned light-rail line will mostly fatten the wallets of developers. The new homes are priced far beyond the reach of lower-income, transit-dependent residents — the very people whom Maryland officials cited in justifying billions of public investment in the 16-mile project.

But the swanky suburban townhouses are part of a larger public-private effort to address what has traditionally been a more urban problem: how to prevent the benefits of transit-oriented living from going primarily to the well-to-do — and pricing out the very people it’s most intended to serve.

“So far, the funding is only there to build the [Purple Line] system, not to go beyond the tracks to address housing or economic development,” said Clarence J. Snuggs, director of Montgomery County’s Department of Housing and Community Affairs.

[Suburbs rethink transit to court millennials]

Construction continues on luxury apartments being built next to the Wiehle-Reston Metro station on the Silver Line. (Pete Marovich/For The Washington Post)

In Chevy Chase Lake, the Montgomery Housing Opportunities Commission, which supplies low- and moderate-income housing in the county, had older garden apartments on almost five acres adjacent to the future Purple Line station site, just off Connecticut Avenue. The land became more valuable as the light-rail project wound its way through the approval process. It also caught the attention of developers, who urged county officials seeking to concentrate new building around transit stations to greatly increase the amount of density allowed there.

EYA, a local developer that has built affordable housing in Alexandria and the District, bought part of the HOC property and tore down the garden apartments to build the luxury townhouses. Working with EYA and the Cafritz Foundation, HOC is using proceeds from the land sale to help build a 200-unit apartment building adjacent to the new townhouses. The additional below-market-rate units in the building and a county law requiring that some of the luxury townhouses be priced below market rate will leave the pricey community with 90 new affordable and workforce housing units — a net gain of 22 above what was there before and more overall for lower-income families. Moreover, HOC officials said, they’re near top-notch public schools, transportation, shopping and other amenities.

“This was a good opportunity,” said Shauna Sorrells, HOC’s director of legislative and public affairs. “We get more units of a higher quality and deeper affordability, all with mixed incomes.”

The issue, which some experts call “transit-induced gentrification,” is gaining new attention in Montgomery and other once auto-centric suburbs building light-rail and rapid bus lines to revitalize older areas, attract younger workers, and help an increasing number of lower-income residents reach jobs. Focusing growth around transit stations has become the way many inner suburbs plan to thrive without adding to the sprawl that has left them drowning in traffic.

The Purple Line project remains ensnared in a federal lawsuit over its potential environmental impacts, and trains aren’t expected to carry passengers for at least five years. But government officials, nonprofit groups and some developers are already strategizing how to prevent the $2 billion line from inadvertently creating a swath of suburban wealth that could upend long-standing communities and leave the line underutilized.

“Being able to have affordable, reliable and safe transit is critical for a lot of communities, particularly low-income communities because they need that option,” said David Bowers, of the nonprofit Enterprise Community Partners. “But we need policymakers and leaders to be much more intentional about preserving affordable housing along those corridors.”

[Purple Line advocates draft ‘community compact’ for route]

Ideally, proponents say, expanding transit most benefits people of lower incomes, particularly in the sprawling suburbs, because more can forego the expense of owning a car. That leaves them more money for rent or mortgage payments.

But suburban transit-oriented living, in high demand from millennials and empty-nest baby boomers looking to downsize, is in such short supply that it commands premium prices — and can encourage property owners to cash in by selling, redeveloping or raising rents.

Gerrit Knaap, director of the National Center for Smart Growth Research and Education at the University of Maryland, is heading a coalition of public officials and private and nonprofit groups that is keeping tabs on the Purple Line project’s social and economic impacts.

The center, on behalf of the group, is monitoring rents, employment, median incomes and other trends along the 16-mile alignment — both before and after the line is built. Knaap said the coalition will use that data to seek financial help from the private sector, nonprofits and foundations if or when residents and small-business owners begin to get priced out.

“There will be pressures for that to happen,” Knaap said. “Let’s be honest. Do we have policies to prevent that from happening? We don’t know.”

In Northern Virginia, new upscale high-rises are popping up at the two-year-old Silver Line Metro stations in Tysons Corner. Officials are already having to tweak relatively new affordable-housing rules aimed at apartment buildings that boast rooftop swimming pools — and one-bedroom units renting at $1,800 to $3,000 per month.

[Metro jump-started Tysons boom, and some say it’s too much too soon]

Officials say Tysons needs housing for people of all incomes if it is to transform from a hub of sterile office buildings and crippling traffic into a more residential community where people can live closer to work and take Metro instead of drive.

Michelle Krocker, executive director of the Northern Virginia Affordable Housing Alliance, said the waiters and clerks in the new restaurants and stores that new Tysons residents will want won’t take — or keep — those jobs if they have to slog through traffic from far away. Krocker said she’s urging Fairfax County officials to consider building below-market-rate homes in conjunction with fire stations, community centers and other public facilities that Tysons will need as it evolves into a more livable community. In particularly short supply are reasonable rents for people with household incomes of about $60,000 and less, she said.

“None of these [new] rent levels are affordable for people who make $45,000 to $50,000 a year, not to mention people who make much less than that,” Krocker said. “Unless you want gridlock with thousands and thousands of cars pouring into Tysons every day, we need opportunities for all workers to have the opportunity to live there. It just makes good economic sense.”

In exchange for allowing taller and larger buildings within a quarter-mile of the Silver Line stations, the county expects new residential buildings in Tysons to have 20 percent of the units set aside as affordable or workforce housing. Developers of new commercial buildings also must contribute $3 per square foot to a Tysons affordable housing fund.

But county leaders are considering relaxing the 20 percent expectation for high-rise condominium projects, after developers complained that it will make it harder to secure financing for their typically smaller buildings. Some said they expect they’ll have trouble selling units in the same building at significantly different prices, and they’ll have no control over condo fees that could rise in time and make lower-cost units suddenly exceed affordability limits.

“Everyone wants more workforce housing, but we’re still trying to figure out how to implement it,” said Michael Caplin, president of Tysons Partnership, a group of business, civic and government leaders.

[Why companies are spending millions to move a mile in Tysons]

In Maryland, helping the people who will ride a Purple Line the most live within walking distance of its stations will probably be a key factor in how much the state will have to pay to subsidize its operations, as transit systems generally require. Unlike most suburban Metro stations, 17 of the 21 Purple Line stations won’t have parking, leaving most riders to reach them by walking or bus.

Affordable-housing advocates are most concerned about rising rents pushing out residents in the lower-income communities of Langley Park in Prince George’s County and Long Branch in Montgomery — a stretch known as the “international corridor” because of its concentration of relatively recent immigrants.

Del. Alonzo T. Washington (D-Prince George’s), who also works on housing issues for CASA, said the organization has pushed for a Purple Line but worries about the 5,000 older homes that “people can barely afford” today in Langley Park.

“We have a lot of working families in Langley Park who will benefit significantly from new transit,” Washington said. “But if they’re displaced from this area and can’t afford to live here, then it doesn’t benefit them at all.”