California air quality regulators say homes should be built at least 500 feet away from freeways.
But some environmental experts say freeway pollution can reach homes much farther away, about 10 times as far.
And long-term exposure can increase health risks like asthma and cardiovascular disease.
Suzanne Paulson is an atmospheric chemistry professor at UCLA. She has some answers to why this pollution has such a far reach.
"We typically have a sea breeze during the day. But at night, we have a weak breeze that goes from the land to the ocean. At the same time, the atmosphere does a poor job of dispersing pollution, and that weak breeze creates a plume that creeps along the ground toward the ocean."
But there are also some common sense ways to protect ourselves. Getting a high efficiency particulate air (HEPA) filter is one way to lower pollution concentration in your home. When driving, set your dashboard vents to circulate air from inside the car.
For runners or other outdoorsy types, Paulson says you're good to exercise outside--depending on whether you're downwind of freeway traffic.
"There's only one side of the freeway that's impacted at any given time. If you can figure out which side that is, exercising or going out on the other side is fine."
Paulson also has good news for cyclists. As L.A. builds more bike paths apart from busy roads, cyclists are also getting more pollution protection while doing their part for the environment.
But Paulson says, no matter what, any distance from pollution is a good thing.
"You don't need to be that far away to reduce exposures a lot. Even if you're just 10 feet away [from roadways] sometimes pollution can be much lower."