The Philadelphia region is one of the nation's most affordable places for moderate-income residents because of relatively low housing and transportation costs, according to a study being released Thursday.

But moderate-income residents here, like those in other metro areas around the country, face costs that are rising faster than their incomes, the study found.

The study of housing and transportation costs in the 25 largest metro areas was conducted by the Center for Housing Policy in Washington and the Center for Neighborhood Technology in Chicago, which advocate for policies to increase affordable housing.

Philadelphia was ranked the second-most-affordable region for moderate-income homeowners and the fifth for moderate-income renters.

"Moderate income" was defined as 50 percent to 100 percent of the median income in the 11-county region: $31,921 to $63,843 a year.

On average, people at that financial level pay 27.7 percent of their income on housing costs and 24.5 percent on transportation costs, the study found.

Housing costs include utilities and upkeep of residences, and transportation costs include train or bus travel or the cost of owning, fueling and keeping a car in repair.

For moderate-income renters, the average monthly housing cost was $961 and the average monthly transportation cost was $832. For moderate-income homeowners, housing cost $1,124 and transportation $1,035 each month.

Between 2000 and 2010, housing and transportation costs for moderate-income residents in the region rose 39 percent, but incomes did not keep pace, rising 27 percent, the study found.

Only the Washington metro area, with high incomes and high housing costs but low transportation costs, was rated more affordable for moderate-income residents than the Philadelphia region.

The Philadelphia area "benefits in modest ways from the costs going in the right direction - housing is somewhat more affordable, transportation is somewhat more affordable, and incomes are somewhat higher than average," said Jeffrey Lubell, executive director of the Center for Housing Policy, and a coauthor of the report.

The Miami area was deemed the least affordable for moderate-income residents, with Los Angeles, San Diego, and Atlanta close behind.

With compact communities close to public transit, much of the Philadelphia region offers relatively inexpensive housing and car-free transportation. But the study authors acknowledged the most affordable neighborhoods are not necessarily the most desirable.

"In practice, many of the most affordable neighborhoods for moderate-income households (for example, North Philadelphia or Camden) are in reality not occupied by moderate-income households but are instead home to very-low-income households," the report said.

"We are only looking at whether housing and transportation costs are affordable," Lubell said. "We acknowledge there are a lot of other things people take into consideration ... such as quality of schools, open space and parks, access to fresh foods."

Unsurprisingly, the study found that higher-income households spent less of their total income on housing and transportation.

Among the 25 metro areas, households with an annual income of about $108,000 spent 20 percent on housing and 13 percent on transportation, compared with 32 percent and 27 percent, respectively, for households with incomes of about $45,000.

"With housing and transportation consuming 59 percent of household income, moderate-income households have relatively little left over for expenses such as food, education, and health care, not to mention savings to cushion unexpected financial hardships," the study authors wrote.

To help moderate-income families, policymakers should support affordable housing close to job centers and public transit, the study said.

"If you want to move the affordability dial, you have to look at both housing and transportation," Lubell said.