WASHINGTON -- A century from now there will be twice as many Americans as today, the Census Bureau predicts.

While no one knows what daily life will be like in 100 years, the new population projections being issued today conjure images of twice as many cars jostling for position on the highways and twice as many shoppers crowding the aisles at Wal-Mart.

From an estimated 275 million people today, the bureau projects a U.S. population of 571 million in the year 2100. That might not seem terribly crowded, however, because the nation is so sprawling.

"If you look at the density for the United States, we are not even coming close to the densities that you see in Europe," said Census statistician Tammany J. Mulder.

The U.S. population density in 2100 would be 161.4 people per square mile, about one-fourth the current population density of Germany and the United Kingdom, Mulder said.

The increase is expected even though childbearing rates in the United States are only about what is necessary to replace the current population.

"The increasing number of potential parents and continued migration from abroad would be sufficient to add nearly 300 million people during the next century," said Census Bureau analyst Frederick W. Hollmann.

Overall, the population will be older -- with some 5.3 million folks over the age of 100 -- and include a larger share of minorities, led by Hispanics.

"Because the Hispanic and Asian and Pacific Islander populations in the U.S. are younger than the nation as a whole and because they continue to receive international migrants, these populations will become increasingly prominent," Hollmann said.

The Census projection calls for the nation's population to probably reach 300 million in 2011, 400 million in 2049 and 500 million in 2081.

By comparison, the U.S. population was 5.3 million in 1800 and 75.9 million in 1900.

The United Nations, in its own projections, expects the world's population to rise from the current 6 billion to about 9.4 billion in 2100.

The age breakdown of America would look different in 2100, Mulder noted, with a more uniform distribution and more elderly people as medical care lengthens lifespan.

For example, currently the Baby Boom generation creates a bulge in the U.S. population at ages 35 to 39 and 40 to 44, the only two segments making up more than 8 percent of the total. And today's population includes just 65,000 people aged 100 and over, 0.02 percent of the total.

By 2100 the over-100 crowd is expected to grow to 0.9 percent of the total, and no five-year age group will even reach 7 percent of all Americans.

The largest age group is expected to be those aged 15 to 19, at 6.4 percent.

The projections show an especially rapid surge in the elderly population as the surviving baby boomers pass age 65. In the year 2011, baby boomers -- those born between 1946 and 1964 -- will begin turning 65.

Between 2011 and 2030, the number of elderly would rise from 40.4 million, 13 percent of the population, to 70.3 million, 20 percent of the population.

The projections call for the number of children under 18 to increase from 70.2 million in 1999 to 95.7 million in 2050. The median age in 2100 is expected to be 40.3, compared to the current 35.8. Median means half of all Americans will be older than that and half younger.

Projections about race include:

l The Hispanic population is expected to triple from 31.4 million in 1999 to 98.2 million in 2050. Hispanics could become the nation's largest minority group with their percentage rising from 12 percent in 1999 to 24 percent in 2050.

l The Asian and Pacific Islander population, meanwhile, would more than triple, from 10.9 million in 1999 to 37.6 million in 2050. Its percentage of the total population would rise from 4 percent now to 9 percent in 2050.

l The non-Hispanic white population would rise 9 percent, from 196.1 million in 1999 to 213.0 million in 2050. Its share of the total population would decline, however, from 72 percent in 1999 to 53 percent in 2050.

l The black population would rise from 34.9 million in 1999 to 59.2 million in 2050, a 70-percent increase. Under this projection,the black share of the total population would increase slightly, from 13 percent to 15 percent.

The projections for racial and ethnic groups are given only through 2050 because they are considered less reliable for the latter parts of the century.

Between 1999 and 2050, the total number of foreign-born Americans would more than double, from 26 million to 53.8 million, to make up 13 percent of the population.

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