If you’ve regularly bicycled in a city you know the scene. You’re trying to stay in the bike lane, or maybe make it through some cars to take an already nerve-wrecking left turn, and a car seems to go faster behind you, not slower, as if to intentionally make your life harder.

Researchers have now found an explanation for why many drivers act out toward cyclists: They are actually dehumanizing people who ride bikes, according to an April study by Australian researchers in the journal Transportation Research. And this dehumanization—the belief that a group of people are less than human—correlates to drivers’ self-reported aggressive behavior.

Since 2010, cyclist fatalities have increased by 25 percent in the US. A total of 777 bicyclists were killed in crashes with drivers in 2017, and 45,000 were injured from crashes in 2015. Data compiled by the League of American Bicyclists also suggests that, in some states, bicyclists are overrepresented in the number of traffic fatalities.

“The idea is that if you don’t see a group of people as fully human, then you’re more likely to be aggressive toward them,” said Narelle Haworth, a professor and director of the Centre for Accident Research and Road Safety at Queensland University of Technology, one of the authors of the study.

The researchers asked 442 Australians, including those who identified as cyclists, to rank the average cyclist on a scale from ape to human. This ape-to-human diagram has been used in other studies, like this one from 2015, looking at the dehumanization of marginalized groups, such as Muslims and black people.

Participants were also asked to rank cyclists on a similar scale showing cockroach-to-human evolution because of the disparaging language that’s sometimes used against cyclists comparing them to cockroaches, the researchers said. Last spring, for example, The Courier-Mail published an anti-bike opinion piece in which the writer said, “[Australian politician] Derryn Hinch once famously referred to cyclists as cockroaches on wheels, and I’m beginning to understand his point of view.”

Then there are views advocating for downright violence against cyclists. The study also noted a 2016 speech in which the CEO of Ryanair said, ‘‘We should take the cyclists out and shoot them.”

In both models, more than half of respondents said they do not consider cyclists to be fully human. Of the participants, non-cyclists rated the average cyclist as only 45 percent human, while those who identified as cyclists themselves rated the average cyclist as 70 percent human in a combined score for both models.

That means even cyclists dehumanize other cyclists. Haworth told me that might be because the study asked respondents about the average cyclist, and “maybe they thought of the average cyclist as different as them. In Australia, a lot of on road riding is done by middle-aged males in Lycra. So I think maybe they thought of this stereotype.”

Researchers said this perspective around dehumanization is directly linked to the way drivers behave toward cyclists. According to the study, 17 percent of respondents self-reported that they had used their car to deliberately block a cyclist, 11 percent said that they had driven close to a cyclist on purpose, and 9 percent that they deliberately cut off a cyclist. These were considered aggressive behaviors, rather than just harrassment like yelling.

It’s often difficult to figure out who’s to blame when vehicle-cyclists accidents and fatalities happen, the Federal Highway Administration told NPR in 2011. While some local agencies in the US have faulted cyclists more often than drivers, as NPR reported, a 2014 report by the League of American Bicyclists showed that 52 percent of cyclists fatalities were caused by rear end collisions and a car’s front hitting a cyclists’ side. And, at least one study in Australia and one examination of UK data shows that drivers are usually at fault.

In the Queensland study, one finding also suggests that, as more cities push and encourage people to bike, drivers’ aggressive behavior could actually worsen with frequency of exposure. Drivers who drove by cyclists at least once a week self-reported four times more aggressive behavior toward them compared to drivers who drove past cyclists less frequently.

Study co-author Nicholas Haslam of the Melbourne School of Psychological Sciences told me this might be because “people who drive [near cyclists] more often just have more opportunities to behave badly towards cyclists, so they report greater numbers of aggressions.”