A new study appears to offer additional evidence that drivers are less likely to brake for African-American pedestrians trying to cross the street, a phenomenon known as “walking while black.”

Researchers at the University of Nevada, Las Vegas also found that the disparity is greater depending on whether the pedestrian is in a high- or low-income neighbourhood: the average number of vehicles to pass by a black pedestrian who was already in the crosswalk was at least seven times higher compared with a white pedestrian in the wealthier neighbourhood, the study’s lead researcher said.

“Sadly, it wasn’t surprising,” said Courtney Coughenour, an assistant professor in the School of Community Health Sciences at the University of Nevada, Las Vegas.

But there are also several factors in the Las Vegas study that suggest the results should be interpreted with care.

In three scenarios that the researchers used, they found little statistically significant data to suggest a difference in the way motorists reacted to the pedestrian, whether black or white. In one of those, in fact, more cars passed the white pedestrian than the black pedestrian when they were waiting to step off the curb in the high-income neighbourhood.

What’s more, the roadways between the high- and low-income neighbourhoods differed in design, both in the number of lanes the pedestrian had to cross and the posted speed limit, as the study acknowledges. The researchers also noted, citing other research, that the disparity between yielding rates in the different neighbourhoods could be explained by several factors, such as people in high-income areas more often having private cars and driving more compared to people in low-income neighbourhoods, where there are also generally more pedestrians.

More than 4,700 pedestrians were killed in traffic crashes in 2013, according to the Centers for Disease Control and Prevention, citing the most recent figures available. The Las Vegas study, also citing CDC data, says fatality rates for black and Latino men are more than twice as high as for white men.

The Las Vegas study, which was published online in January in the journal of Accident Analysis and Prevention, involved observing what happens when two female students — one black, one white — cross a street where there is no traffic light.

The experiment was conducted in one neighbourhood located on the west side of Las Vegas where the median household income was $55,994, and in another in the east where the median was $32,884. (Coughenour declined to identify the two neighbourhoods further.)

Both pedestrians in the experiment were students and both were of similar height and build. Each wore similar clothing. They took turns crossing the street about 126 times, or approximately 34 times in the high-income neighbourhood and 30 times in the low-income neighbourhood. (Two crossings were spoiled by observer error.)

The researchers first counted how many cars passed while the pedestrian stood on the curb waiting to cross. After the first car stopped in the nearest lane and the pedestrian stepped into the street, observers continued to count vehicles that failed to stop in the remaining lanes on that half of the street. (The observers did not count traffic moving in the opposite direction on the other half of the roadway.)

What the researchers found was that drivers yielded to the pedestrian waiting at the curb to cross about 52 per cent of the time in the high-income neighbourhood and 71 per cent of the time in the low-income neighbourhood.

After factoring in race, the researchers found little statistical significance in whether drivers yielded for black or white pedestrians waiting at the curb in either neighbourhood — although drivers in the high-income area were less likely to yield for the white pedestrian. (And a higher percentage of drivers in the low-income neighbourhood stopped for the white pedestrian.)

But Coughenour said she was much more troubled by the what happened when the pedestrians stepped off the curb and began walking in the crosswalk — both because of the more dangerous circumstances and because the statistical significance was higher: The average number of drivers who continued moving with a black pedestrian already in the crosswalk was at least seven times higher than for the white pedestrian in the high-income neighbourhood, she said.

Among the several caveats worth noting are these, however:

Nevada law is ambiguous about when drivers are required to stop for pedestrians. Under state law, when there is no traffic light, for example, a driver is obliged to slow and yield the right of way “if need be” when a pedestrian is in the crosswalk on the same half of the highway, the study says. They are also required only to “exercise proper caution” when observing a pedestrian on or near the roadway.

The crosswalk in the high-income neighbourhood was on a street with six lanes and a speed limit of 45 mph (72 km/hr.); the street in the low-income neighbourhood had four lanes with a 35-mph speed limit.

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The observers were aware of whether a black student or a white student was crossing. To control for possible observational bias, however, the observers followed a protocol for making observations and counting passing cars, Coughnenour said.

The sample size is relatively small.

Coughenour, while acknowledging the study’s limitations, said she believes the results confirm what researchers found in a study conducted by researchers at Portland State University in Oregon and the University of Arizona. She said the findings are also in line with a large body of literature that suggests people react differently to others based on “implicit bias” that may not be conscious. “We all have some sort of innate bias,” she said.