The 50 states and the District of Columbia spend a combined $3.6 billion each year enforcing bans on marijuana while arrest disparities continue to increase along racial lines, according to a report purporting to show how prohibiting the drug has failed.

"The War on Marijuana in Black and White," from the American Civil Liberties Union used statistics from the FBI's Uniform Crime Reporting Program and the U.S. Census, among other sources. It purports to also show how arrest rates have risen steadily for 10 years, despite pot usage and its availability being at an all-time high.

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"To the extent that the goal of these hundreds of thousands of arrests has been to curb the availability or consumption of marijuana, they have failed," the ACLU reported, adding continued enforcement "served as a vehicle for police to target communities of color."

Between 2001 and 2010, the overall number of marijuana arrests has risen steadily, now accounting for 52 percent of all drug-related arrests in the United States, but the study's authors conclude that increase has been linked almost solely to an increase in the arrest rate of blacks.

The minority community is nearly four times more likely to be arrested for possession than whites, according to the report. While arrests for whites have remained fairly constant at around 192 arrests per 100,000 Americans, arrests for blacks have risen from 537 to 716.

The disparity exists regardless of household income but is more prevalent in middle-class and wealthier communities, the report found. But the rate of usage remained roughly equal between blacks and whites, said the report.

New York and Washington, D.C., share the top two arrest rates per capita, with 846 and 535 arrests respectively per 100,000 residents.

The ACLU said police made 889,133 pot-related arrests in 2010, or one every 33 seconds. The states foot approximately $3.6 billion of the costs divided between the cost of policing, adjudication and incarceration of those convicted.

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The report comes as national polls suggest a majority of Americans support lifting the federal prohibition on the drug. A recent Pew survey found that 52 percent support legalization, while 45 percent oppose it. Roughly half of Americans admitted to smoking marijuana at least once in their lifetimes, with 12 percent admitting to smoking pot in the past year.

Two states have currently approved marijuana for recreational use: Washington and Colorado. An additional 12 have passed measures that allow marijuana for limited medical purposes. The state laws have on occasion come into conflict with the existing federal ban, although the Obama administration has stated it would not actively pursue enforcement over state law.