Voters who live in predominantly black neighborhoods faced significantly longer wait times to cast a ballot than those who live in predominantly white neighborhoods, a new study finds.

The research, conducted by economists and statisticians at UCLA, Carnegie Mellon University and the University of Chicago, used smartphone data that showed how long more than 150,000 devices had spent at specific polling places across the country as a way to measure how long the owners of those smartphones waited to vote.

The study mapped more than 93,000 polling places, or about 80 percent of those open on Election Day 2016.

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The average voter spent 19 minutes at a polling place in 2016, the study found, while some 18 percent of voters spent more than half an hour waiting to vote. Voters were more likely to find themselves in long lines early in the morning, when average wait times neared 30 minutes.

But the longest average wait times came in census blocks with higher percentages of African American voters. The difference between a census block with no black residents and a census block with all African American residents translated to an extra five minutes of waiting time, the study found.

And those voters in heavily black neighborhoods are most likely to wait in long lines. Residents of entirely black areas were 74 percent more likely to have to wait more than 30 minutes to cast their ballot than residents in entirely white neighborhoods.

“We find substantial and significant evidence of racial disparities in voter wait times,” the study’s authors concluded.

The study comes just as the Leadership Conference Education Fund, an arm of the Leadership Conference on Civil and Human Rights, reported a wave of polling places closing in states across the South in the years after the Supreme Court overturned a key provision of the Voting Rights Act.

That report found counties and cities once covered under Section 5 of the Voting Rights Act had closed at least 1,688 polling places between 2012 and 2018. Between 2014 and 2018, there were 1,173 fewer polling places in those areas, even though voter turnout had increased.

“While there are justifiable reasons for closing polling places, the sheer scale of closures we have identified since [the Supreme Court’s decision in Shelby County v. Holder] coupled with other stark efforts to deny voting rights to people of color demand a response,” said Vanita Gupta, president and CEO of the Leadership Conference on Civil and Human Rights.

The counties that closed the highest number of polling places since the Supreme Court decision were disproportionately likely to have diverse populations. Maricopa County, Arizona, home of Phoenix, closed 171 voting locations since 2012, the report found; nearly one-third of Maricopa residents are Latino. Dallas County, Texas, a majority-minority county, closed 74 polling sites.

In Georgia, then-Secretary of State Brian Kemp — now the state’s governor — explicitly told county elections officials they were no longer required to seek pre-clearance from the Justice Department before they made changes to polling locations. Three Georgia counties closed more than 80 percent of their polling places in the years after the Supreme Court’s decision.

--This report was updated on Sept. 12 at 10:57 a.m.