Transit-oriented development – the clustering of homes, shops and services around transit hubs like rail stations and bus terminals – is intended to promote a more healthful lifestyle. But not all transit villages are created equal. Oakland’s next big experiment in transit-oriented development may be overshadowed, literally and figuratively, by the city’s freeways.

Among urban planners, the conventional wisdom is that creating an appealing environment and clustering services together will encourage people to walk and bike. Transit villages, as transit-oriented developments are often called, try to recreate, artificially, the benefits of high-density living found naturally in most cities’ downtowns: energy efficiency, access to public transit, thriving retail, and sometimes even a sense of community.

To date there are three completed transit villages along BART rail lines (at Fruitvale, Hayward, and Pleasant Hill), another three under construction (including MacArthur), and six more in various stages of planning. If all of these projects are carried out, more than a quarter of all BART stations will be connected to a transit village.

The best transit villages draw other useful services to the neighborhood. The Fruitvale Transit Village in East Oakland, situated alongside the BART station of the same name, includes a dental office, an optometrist, and a low-cost clinic (not to mention a public library and a charter school). Residents live across the street from a full grocery, and twice a week the village hosts a farmers’ market. If Fruitvale is any indication, transit villages appear to promote a healthy lifestyle from just about every angle.

Except for one. Transit villages are typically built near rail lines, but because rails and roads often run alongside each other, sometimes transit villages pop up uncomfortably close to major highways. The spread of transit-oriented development throughout the Bay is forcing public health experts to look more closely at air quality around these transit hubs. And some research resulting from that closer look suggests the health effects of transit villages may be more mixed than urban planners previously thought.

A few miles north of Fruitvale, a construction firm called Howard S. Wright has begun building a transit village next to the MacArthur BART stop, the busiest station in the BART system. Construction crews are just starting to build the project’s 478-space parking garage. But by the time the village opens in 2021, the station’s parking lot will have transformed into a five-building complex delineated by tree-lined pedestrian streets. The ground floor will house 42,500 square feet of commercial space – likely home to dining and retail, though it’s too early to say exactly who will set up shop. The upper floors will consist of more than 600 one- and two-bedroom apartments, of which about 100 will be rented at below-market rates for low-income residents.

Building next to the MacArthur station means building next to a pair of massive freeway overpasses – State Route 24 and I-580 – and all the pollutants that come with them. Because BART was built at the same time as the Bay Area’s first freeways, many stations – five in the East Bay, three in the South Bay – sit within a few feet of the freeway, as does Caltrain’s South San Francisco stop. The development at MacArthur will be closer to the freeway than any Bay Area transit village to date.

Although this proximity may pose a health risk, BART’s rails were laid alongside the freeway in order minimize the disruption to the communities through which it runs.

“You’ve got to go back to 50 years ago. You’re talking about a community that was already in place. There was already sort of a corridor there,” said Jim Allison, a BART spokesman. “Rather than creating a new corridor, and displacing people from their homes, we tried to make use of an existing corridor.”

Consideration of the existing community is a departure from earlier approaches to development in the area. State Route 24 and the above-grade BART line surrounding the MacArthur station cut off those who lived west of the highway from the thriving Telegraph Avenue corridor. UC Berkeley’s Health Impact Group, which analyzed air quality and other factors that would affect quality of life at a MacArthur Transit village, identified the reintegration of the eastern and western halves of the neighborhood as a high priority. In their 2007 health impact assessment, they found a transit village might help, but it could not fully erase the impact of a freeway cutting through the area.

“Connecting east and west, that’s where we were most critical,” said Dr. Rhajiv Bhatia, lead author of Berkeley’s assessment. “There are engineering solutions for issues like air pollution, but it’s hard to overcome that dividing line.”

Overcoming air pollution, however, may prove difficult in practice.

Commuters who use the MacArthur station spend a few minutes a day on a platform surrounded by the noise and pollution of the freeway. But catching a train next to the freeway and building a home under one represent two drastically different levels of exposure to a highway’s worth of vehicle emissions.

A block south of MacArthur, Elouise Bradley has spent the last 35 years in a house wedged as close to State Route 24 and I-580 as any in Oakland. On her front stoop, she said that it takes no small effort to keep her home clean.

“There’s a lot of dust and black soot and stuff,” she said, pointing at her yard. “You clean it up, it comes back. You get used to it.”

Bradley’s health hasn’t been affected by the soot, she said. But the pollution is a public health concern.

Cars and trucks emit soot-like particles capable of penetrating deep into one’s lungs. Public health analysts pay special attention to particles that are less than 2.5 micrometers wide – about the width of a hair – which are called “fine particulate matter,” or PM2.5. With enough exposure, PM2.5 can lead to asthma, chronic wheezing, reduced lung capacity and lung cancer.

The Environmental Protection Agency considers a daily average of 15 micrograms of PM2.5 or less per cubic meter to be safe. Fortunately for MacArthur’s future residents, PM2.5 levels around the planned transit village are well below this threshold. Levels around the site hover at just 0.3 micrograms, according to UC Berkeley’s health impact assessment.

That does not, however, mean that the area poses no risk to residents’ respiratory health. UC Berkeley’s assessment found that the PM2.5 levels around MacArthur contribute to 2.7 “excess” deaths annually per 100,000 people exposed, as well as 34 cases of acute bronchitis, 214 sick days, and 1,136 cases of “minor restricted activity.”

Furthermore, a 2010 study found that PM2.5 may contribute to diabetes, even at levels considered safe by the EPA.

Of ten strategies Berkeley researchers recommended to promote respiratory health around the MacArthur BART, only one – high-efficiency filters on the buildings’ ventilation systems – would directly address the pollution coming from the freeways. But filters would not protect residents in the complex’s many courtyards and pedestrian streets.

Their other recommendations, from “unbundling” parking from the cost of a residential unit to using electric-powered forklifts, do nothing to mitigate the major source of pollution around the development.

The report goes so far as to suggest, bluntly, “notifying all potential buyers the property they are buying has air quality risks.”

The MacArthur village will leave its residents very little breathing room. Going up at one end of the BART station’s parking lot, the housing development will be separated from State Route 24 by just a narrow access road, or about twenty feet. For comparison, the much-touted Fruitvale village is separated from I-880, the nearest freeway, by about 1,000 feet.

MacArthur’s transit village, with 624 residential units, will also be significantly larger than Fruitvale, which has just 47 units (and a long waiting list, though there are plans to expand the complex).

The MacArthur transit village may not be complete for a decade, or longer. But the effects of two freeways’ exhaust are already clear on the buildings that surround the construction site. Just across MacArthur Boulevard, the walls and windows of a once-white apartment complex are caked in black grime.