Los Angeles is the world's most congested city. In 2018, LA placed first for the seventh year in a row for being the most gridlocked city with commuters spending just over four days a year sitting in traffic last year, according to research by Inrix Global Traffic Scorecard.

That traffic is costly. It cost LA drivers more than $2,800 in fuel and time in 2017, says Inrix. In total in 2017, all that congestion cost the city of Los Angeles over $19 billion.

The gridlock doesn't just have an economic cost, it also hurts the environment.

"The air quality is still very much sub-standard in Los Angeles County and a lot of that is due to transportation," says Gabe Kahn, a USC professor and editor of Crosstown, an organization studying traffic and crime data in LA.

Accordingly, in 2017 about a third of the US's greenhouse gas emissions were from the transportation sector, according to the Environmental Protection Agency.

LA Metro is working to decrease those emissions. Chris Libon, LA Metro's executive officer for Environmental Compliance and Sustainability, says LA Metro has the largest clean air fleet in the country.

"This time next year we expect to be 100% renewable natural gas in terms of our propulsion power," says Libon.

Still, however, much of the fight for cleaner air in LA will require Angelinos to ditch their cars. This could be a problem for LA natives who owned almost eight million vehicles in 2017.

"What you really need is an unpalatable alternative to public transportation," says Kahn. "If freeways become so unpleasant, more people will take public transportation."