Urban sprawl doesn't just mean more time in the car, it could also mean a shorter life.

Residents in more sprawling cities were likely to have fewer economic opportunities, be less healthy and have shorter life spans compared to people in more compact areas, according to a report released Wednesday by Smart Growth America.

For example, the more compact a city, the greater the chances that a child born in poverty will become rich. Similarly, the report found a three-year difference in life expectancy between residents in the most sprawling parts of the country versus the most compact.

"How we develop has a huge connection to how healthy we are in our communities," said Ilana Preuss, Smart Growth's chief of staff. However, she stressed that just because sprawl is related to negative social conditions, it does not necessarily cause them.

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To calculate sprawl, the organization, which promotes reinvestment in existing cities, looked at four things:

-- The density of houses and jobs

-- The mix of residential and commercial buildings (the greater the mix, the better)

-- The concentration of residential and commercial developments in downtown or other "activity" areas, like a waterfront

-- The "accessibility" of streets, including the length of blocks (the shorter the better, because it means more cross walks) and the number of four-way intersections (the more the better because it means greater street connectivity)

The researchers then cross-referenced these data points with data on economic mobility, life expectancy and other similar metrics to reach their conclusions. Most of the data came from the Census Department.

On a conference call discussing the report, researchers noted that cheap land in some places encourages sprawl. Also, many cities that fared well on the list, like San Francisco and New York, are bound by water or mountains, and thus have a hard time expanding outward.

Other cities like Los Angeles and Trenton, N.J., had policies that encourage denser development or more walkability through zoning or other incentives for developers.

"We need to look in great detail in how we're making development decisions," said Preuss. "We're very much in control of these things."

The study looked at 221 metropolitan areas with a population of at least 200,000 people. The research was done in conjunction with the University of Utah's Metropolitan Research Center and prepared for the National Cancer Institute at the National Institutes of Health and the Ford Foundation. It was an update to numbers originally published in 2002.

While housing costs tend to be higher in more compact areas, transportation costs tend to be lower. When factored together, it can actually be relatively cheaper to live in a more compact city.

For example, an average household in sprawling Tampa, Fla., spends 56% of its budget on housing and transportation, while an average household in more compact Seattle spends only 48% of its budget on the same items, the report said.