Fifty years after the creation of the Department of Housing and Urban Development — and nearly that long after the passage of the Fair Housing Act of 1968 — the fight against the interlinked scourges of housing discrimination and racial segregation in America is far from finished. Economic isolation is actually growing worse across the country, as more and more minority families find themselves trapped in high-poverty neighborhoods without decent housing, schools or jobs, and with few avenues of escape.

This did not happen by accident. It is a direct consequence of federal, state and local housing policies that encourage — indeed, subsidize — racial and economic segregation. Fair housing advocates have recently been encouraged by a Supreme Court decision and new federal rules they see as favorable to their cause. Even so, there will be no fundamental change without the dismantling of policies that isolate the poor and that Paul Jargowsky, a professor of public policy at Rutgers University-Camden, and others call the “architecture of segregation.”

As things stand now, federally subsidized housing for low-income citizens, which seems on its face to be a good thing, is disproportionately built in poor areas offering no work, underperforming schools and limited opportunity. Zoning laws in newer suburbs that rest on and benefit from infrastructure built with public subsidies prevent poor, moderate-income and minority families from moving in. Discriminatory practices exclude even higher income minority citizens from some communities.

The economic expansion of the 1990s brought wage increases and low unemployment, diluting poverty and cutting the number of people living in high-poverty neighborhoods by about 25 percent. Many policy experts believed at the time that the era of urban decay was coming to an end. But as Mr. Jargowsky observes, that’s not how things worked out. In a new analysis of census data, he finds that the number of people living in high-poverty slums, where 40 percent or more of the residents live below the poverty level, has nearly doubled since 2000.