Cities are bigger than ever and, for many, the car is the only conceivable option for getting around them to where they need to be. So how come academics in the city-planning world are advising on changes—like making parking more expensive—that will make it harder to drive rather than easier?

Turns out there are lots of reasons—and most center on health.

“Private motor vehicle sales are often used as an indicator of economic growth, development, and modernisation,” researchers from universities in Australia, the US, and Brazil detailed in a series of research papers published last week in the Lancet medical journal.

Worldwide, they said, road traffic accidents are the eighth-biggest cause of ill-health and death, as expressed in “disability-adjusted life years,” or DALYs, an overall measure of years lost to disease, injury, and early death. Deaths from road transport injuries exceed those from HIV and AIDS, tuberculosis, and malaria, according to a 2014 World Bank study.

What’s more, as people continue to move to cities and urban populations thereby become denser, the problem is getting worse. “By 2030, road traffic injury-related DALYs are estimated to be more than 10 times those of tuberculosis and malaria combined and twice those of HIV/AIDS,” the researchers wrote. Meanwhile, young people including children, older people, and poor people who are less likely to have access to their own car are more likely to be hurt or killed in traffic accidents.

The alternative is to improve public transport, and encourage walking and cycling while simultaneously planning cities so that they are more compact, reducing the overall distance people have to travel to work or school.

The problem with walking and cycling, though, is that the dominance of cars mean more people could get hurt and injured until a critical mass has been reached. Once the critical mass has been reached, collision rates fall, the researchers said. Encouraging people to be more active, and creating better infrastructure like cycle paths, is one way to achieve the goal.

Another is to make driving less attractive. The researchers look to Germany, France, the Netherlands, and Sweden, which they note managed to reduce injury and death rates for walkers and cyclists by more than 70% between 1975 and 2001. Methods included low speed limits, reduced parking, and liability laws in which more vulnerable road users, not drivers, are assumed to be innocent.

All in all, the reports suggest that city dwellers across the world may need to start saying their farewells to the automobile age.