Ditching cars for buses, bikes, or good ole fashioned walking in cities can reduce pollution by 40 percent by 2050, according to a new study published Wednesday.

The report, by the University of California and the Institute for Transportation and Development Policy (ITDP), proposed improving upon public transportation. This includes expanding rail and bus transport and making sure cities are safer for pedestrians and cyclists.

We all know how dependent we are on our car for getting from A to B, but they are also the fastest growing source of carbon dioxide emissions in the world.

"While every part of the global economy needs to become greener, cleaning up the traffic jams in the world's cities offers the least pain and the most gain," co-author Michael Replogle, ITDP's managing director, told Reuters.

Not only would the move cut carbon dioxide emissions from urban passenger transport by about 40 percent by 2050, but it would also save the economy $100 trillion in public and private spending.

Without intervention, transportation emissions around expanding cities will nearly double from 2010 levels by 2050.

"The traffic congestion we see today will become much greater and will result in many more hours being stuck in traffic," Replogle told BBC News, adding that traffic jams would also have a detrimental impact on nations' economic activity, as people would be late getting to work or meetings.

"People will have to spend much more on transport that will serve them much less well."

And according to United Nations figures released earlier this year, cities are only continuing to grow. About 54 percent of the world population currently lives in cities, and this figure is forecast to rise to 66 percent by 2050, Reuters reports.

"The bottom line message is that to address climate change we really need to undertake all of the measures that are feasible to help us reduce global warming pollution," Replogle added.