The small but provocative study — conducted by researchers at Portland State University in Oregon and the University of Arizona — suggests that biases just outside people’s conscious awareness can make them less likely to yield to minority pedestrians. And that could put those pedestrians at risk, said Kimberly B. Kahn, an assistant professor of social psychology at Portland State University.

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Put another way: Not only do black men have to worry about being hassled — and possibly shot — by police for simply being black, they have to worry about being run over by motorists.

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Kahn said a follow-up study is underway to see whether drivers also discriminate based on gender and whether crosswalk design and signage might change driver behavior.

Implicit bias describes the way that people may unconsciously be biased toward others based on their race, gender or some other group category even if they are not explicitly racist in their thinking.

Yet those subtle biases can emerge when people encounter a stressful situation or make split-second decisions, such as when driving. A U.S. study found that people in expensive or “high-status” vehicles were the least likely to yield to a pedestrian. An Israeli study found that drivers are more likely to yield to pedestrians in their own age group.

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The effect of such subtle biases is complex. But it might cause minority pedestrians to act in ways that put themselves in danger, such as forcing the right-of-way when cars fail to stop for them, Kahn said.

The U.S. Centers for Disease Control and Prevention, citing 10 years of data, says blacks are twice as likely to die in pedestrian accidents than whites, even when controlling for differences such as socioeconomic status and alcohol use.

“We definitely can’t say that the differences in things such as fatality rates can be explained by what we observed,” said Arlie Adkins, an assistant professor at the University of Arizona School of Landscape Architecture and Planning. But Adkins said he believes that over time and with repetition, these slights contribute to risk.

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The study — whose findings were published in August by Transportation Research Part F — took place in downtown Portland, a city of about 600,000 that’s 76 percent white and about 6 percent black.

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A mid-block crossing without signals was selected so that there would be no doubt the drivers were yielding to a pedestrian, and not slowing for an intersection or to make a turn. The crosswalk was marked with zebra striping. The trials were conducted in daylight, so visibility wasn’t an issue.

The researchers used six young men who were black or white to be pedestrians. All of them were in their 20s. Each had a similar height and build, and they wore identical, nondescript clothing: khakis and a long-sleeve gray shirt. They were coached on how and when to approach the crosswalk, with the same pace and posture. They were told to make eye contact with drivers but otherwise be as neutral as possible in their facial expression.

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In 88 trials, a total of 173 drivers passed through the crosswalk, including those who stopped. There was not a huge racial discrepancy in regard to whether the first car to reach the crosswalk would stop for a pedestrians: 55.6 percent stopped for white pedestrians, compared with 48.8 percent for blacks.

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What was more striking, however, was that if the first driver failed to stop for a black pedestrian, several others blew by him, too. In fact, black pedestrians were more than twice as likely to be passed by two or more cars, compared with white pedestrians.

The researchers — Adkins, Kahn and Portland State doctoral student Tara Goddard — said their findings were consistent with research on people’s response to antisocial behavior. That is, if you see people acting badly, you’re more likely to do the same.

“I think what’s really important is first recognizing, or having some initial evidence, that drivers are treating pedestrians differently based on their race and physical appearance,” Kahn said.