Planners in Prince George’s County have talked for years about reshaping communities to help residents fetch a gallon of milk via a walk or bicycle ride, rather than add to stifling traffic congestion by having to drive.

But planners say they’re increasingly treating the Maryland county’s low-density, auto-dependent design as more than a traffic problem. More often, they say, they’re considering sprawl a health hazard.

Nearly 70 percent of Prince George’s adults are considered overweight or obese, and many areas of the county lack sidewalks or feel unsafe — whether from cars or crime — for walking, cycling or playing outside. With some of the longest commutes in the Washington region, planners say, many residents have little time to walk the dog, let alone get to a gym.

Now, in addition to trying to curb traffic, Prince George’s officials talk about changing the county’s “built” environment — how and where buildings, streets and other aspects of new development are laid out — to improve public health.

“We’ve always talked about health and recreation in terms of bicycle access and trails and parks,” said Kierre McCune, a Prince George’s planner. “But now we’re looking at how does our physical development affect our public health?”

A more health-oriented approach to urban planning is taking on new urgency across the United States as rates of child and adult obesity have soared, along with Type 2 diabetes, heart disease and other weight-related illnesses — despite public education campaigns and doctors’ warnings. Last year, U.S. life expectancy declined for the first time since 1993, in part to rising fatalities from heart disease, stroke and diabetes, according to a federal report released earlier this month.

It’s not just physical health. Preserving trees and other green space is cited as key to a community’s mental health, as recent Stanford University studies have found that spending time in nature can boost mood and working memory while reducing brain activity related to depression. In suburbs where garage doors took the place of front porches, experts say, some residents crave social connection.

“People really are beginning to understand . . . what went wrong in how we designed our cities and suburbs over the past 50 years with the dependence on cars,” said Susan Powers, president of Urban Ventures, a Denver firm that’s building a 17-acre, “health-focused” community in the city.

The community, which has some residents, advertises “a healthy lifestyle and simplified living,” including gardens, pocket parks and a network of paths.

While no one can be forced to eat well and exercise, Powers said, “You can create communities where healthy choices are the default, easy thing to do.”

The link between planning and public health is gaining attention at a time when many suburbs are seeking to redevelop corridors of wide streets lined with 1950s-era strip malls, gas stations and parking lots. That car-centric design has proved dangerous for pedestrians and cyclists, planners say. It’s also become increasingly out of vogue, particularly among the outsized demographic groups of millennials and baby boomers, who have shown a preference for more compact, walkable living.

Planners say a focus on health underlies, in part, efforts to widen sidewalks, improve outdoor lighting, and implement “road diets” by allotting more pavement to bike lanes and sidewalks.

In Prince George’s, the Health Department has begun to comment on development proposals, and planners are updating the county’s zoning law to allow homes, office buildings and shopping areas to be built closer together to encourage walking. They’re considering a requirement that developers provide more open space and health-oriented public amenities such as building recreational trails.

In Northern Virginia, Fairfax County recently added “healthy living environment” as a goal of its updated economic development plan. Staffers for the county’s planning, parks and transportation agencies also are tapping public health officials for input earlier in their decision-making.

Fairfax’s health director, Gloria Addo-Ayensu, said the approach is still “a work in progress” but said the county can correct “man-made” obstacles to healthy living.

“People don’t think about it this way, but planning policies, zoning policies, housing policies — they’re all health policies,” Addo-Ayensu said. “It’s a shift in thinking that our non-health sectors are gaining.”

Health officials say people will nod as a doctor advises them to eat better and exercise more — and do none of it if they can’t easily reach a quality grocery store or have safe places to walk, jog or play.

Celeste James, director of community health for Kaiser Permanente’s Mid-Atlantic region, said the company has long known the importance of “place” in a community’s health. A patient’s Zip code, she said, determines life expectancy and overall health far more than genetics or access to health care, largely because of poverty. She said that’s why Kaiser Permanente spent more than $1 million during the past five years to help four lower-income Prince George’s towns — Bladensburg, Colmar Manor, Cottage City and Edmonston — address barriers to healthy eating and physical activity.

“We know we need to address the environments in which our members live, not only their health when they enter our medical centers,” James said.

The Port Towns Community Health Partnership resulted in two new urban farms, a new weekly farmers market, and classes about healthy eating and exercise in local schools, she said. A study of the project couldn’t prove beneficial changes in residents’ health because neighborhood-specific data, such as obesity rates, wasn’t available, James said.

In fact, researchers say data proving that healthier communities make healthier residents is hard to come by. It’s difficult, they say, to pinpoint why someone lost weight, and tracking long-term behavior changes can take years.

But some point to ample anecdotal evidence.

Xuemei Zhu, an associate professor of architecture at Texas A&M University, has been studying residents in Mueller, a 700-acre pedestrian-oriented community being built three miles from Austin. A 2014 pilot study by Zhu and her colleagues found that, in surveys, 65 percent of Mueller residents said they had become more physically active since moving there, and 48 percent said their health had improved.

Zhu said the team is now doing a five-year study, funded by a $2.6 million federal grant, to determine whether such walkable communities actually inspire residents to be more physically active or if residents chose to live there because they were already relatively health-conscious.

She said the first study found that many Mueller residents reported reaching the federally recommended 30 minutes of daily physical activity because they found it easy to take a brisk walk to a coffee shop or play in a park.

In suburban Maryland, Montgomery County planners recently made “habitat and health” one of six “performance areas” of the downtown Bethesda growth plan that is under consideration.

Montgomery’s planning director, Gwen Wright, said the county aspires to “10-minute living,” the ability to reach jobs, stores, schools and entertainment within an “inviting” 10-minute walk.

“I think it’s sort of a mind-set of saying, ‘We’re going to be a community where walking and being in the public realm is easy to do and something [people] want to do,’ ” Wright said. “Maybe you can’t do an exercise class three time per week, but we all know we could walk more.”

Researcher Magda Jean-Louis contributed to this report.