By TIM SHEEHAN

Central Valley Journalism Collaborative

The distinct fragrance of automotive exhaust hangs in the air in the parking lot of a popular commercial corner in north Fresno during a recent weekday lunch rush.

Standing between a pair of fast-food drive-through restaurants, one can observe dozens of cars, pickups and SUVs idling in line as drivers wait to order and then collect their food – burgers and fries at one restaurant, chicken sandwiches and fries at the other.

Creep forward a few feet, stop and wait, tap the gas and creep forward again, stop and wait some more – a cycle, repeated over and over throughout the day, from the time a driver enters the line until they leave the pass-through window with their order.

All the while, fuel-burning vehicles pump into the atmosphere a lush combination of hydrocarbons, oxides of nitrogen and other emissions, including carbon monoxide and carbon dioxide – stuff that contributes to the vehicular effluent often known as “smog.”

Just how much gunk is coming

from those idling tailpipes?

“Honestly, I haven’t thought about it to that extent,” said Bethany DeGough, a Madera Ranchos resident who sat in a long line of vehicles at the In-N-Out Burger restaurant in north Fresno. “I’ve thought about when we’re walking to go inside the restaurant, ‘Oh, it smells like smog,’ that’s occurred to me.”

In addition to components of ozone or smog, a raft of other tailpipe emissions, such as ammonia, benzene, toluene and more, are breathed in by motorists sitting in drive-through lanes, as well as employees who work the drive-through windows and even other diners inside the restaurant.

Each day, cars line up and idle at roughly 1,300 fast-food and coffee drive-through lanes up and down the San Joaquin Valley. But the extent to which they contribute to the degradation of the region’s air quality is a mystery that appears to have so far gone unstudied by regional and state air quality regulators.

In San Joaquin County, of the 197 drive-throughs, 96 are in the city of Stockton. as for the 188 in Stanislaus County, 102 are in the city of Modesto.

(The number of drive-throughs unofficially inventoried by CVJC includes only fast-food and coffee outlets; it does not include numerous other businesses that provide drive-up or drive-through lanes, such as banks or pharmacies, where vehicles may idle while waiting for service.)

Anyone who’s lived in the Valley for even a few months can attest to the region’s stubbornly poor air quality at certain times of the year.

From Stockton and San Joaquin County in the north, to Bakersfield and Kern County in the south, the Valley has long been a “nonattainment region,” meaning it is out of compliance with federal air quality standards for both ozone and PM 2.5 – fine particulate matter about 30 times smaller than the diameter of a human hair that can be inhaled and lodged in human lungs.

Those pollutants and others are often trapped by the mountains that surround the Valley and, under particular atmospheric conditions, turn the region into something that from above looks like a vast, gray lake.

“We know that the amount of fuel that gets burned and the emissions that come out of a gas- or diesel-powered car depends on how fast you're driving, whether you’re driving, whether you’re accelerating, whether you’re idling,” Chris Cappa, a professor in the UC Davis Department of Civil and Environmental Engineering, told the Central Valley Journalism Collaborative in an interview.

Cappa said emissions from idling vehicles in drive-through lanes certainly contribute to the Valley’s air pollution, but pale in comparison to the total emissions generated by everyday driving on streets and highways.

“On a very average condition, when you’re idling, you might not think you’re using a lot of fuel,” he said. “You’re just sitting there. You’re not moving the whole car, but you’re actually still using on the order of a quarter to a third of the same amount of fuel you might be using while driving the same amount of time. So if you’re driving for a minute versus idling for a minute, you’re still using a good amount of fuel. And that will all add up.”

Why does it matter?

A 2025 report by the U.S. Department of Energy’s Argonne National Laboratory in Chicago states that “idling reduces your vehicle’s fuel economy, costs you money, and decreases air quality. Idling for more than 10 seconds uses more fuel than stopping and restarting your engine does.”

Emissions of carbon monoxide, nitrogen oxides, hydrocarbons and volatile organic compounds generated by gasoline- and diesel-powered vehicles, whether at driving speeds or during idling, contribute to the formation of smog or ozone, according to the U.S. Environmental Protection Agency, while carbon dioxide – which represents about 99% of tailpipe emissions, is a primary greenhouse gas contributing to climate change.

A 2025 study of nationwide fast-food restaurants by industry research firm Intouch Insight determined that the average time a driver spent in a drive-through lane was just over 5 ½ minutes, from entering the line through receiving their order.

The amount of time that a driver may spend in a drive-through lane can vary widely depending on the popularity of a particular location, the time of day, the number of vehicles in line, and other factors. But all those minutes add up, particularly in commercial areas and near freeway off-ramps where drive-through sites are clustered together.

Marcel Moran, an assistant professor at San Jose State University’s School of Planning, Policy and Environmental Studies, and his colleagues have sought to inventory every drive-through in the U.S., from restaurants to banks to pharmacies and more – about 130,000 in all.

“What was interesting to us was obviously the big number, but they also really track with population,” Moran said in an interview with CVJC. “They’re really concentrated in urban places, and they’re very clustered. We found that the average drive-through is something like one-tenth of a mile from the next one, and that makes sense if you think about these kinds of high-speed arterial intersections where drive-throughs seem to be on every corner.”

The localized effects of all those drive-throughs are a focus of research by Fengxiang Qiao, a professor of transportation studies at Texas Southern University and co-director of the university’s Innovative Transportation Research Institute. Qiao is one of few researchers who have sought to evaluate how much pollution comes from the tailpipes of idling vehicles when they are queued up in drive-through lanes.

In what appears to be one of the only studies of its kind, Qiao and fellow researchers used specialized equipment to measure the volume of tailpipe emissions per second from test vehicles in drive-through lanes at several fast-food restaurants in the Houston area. That 2016 research shows that pollution levels vary depending on whether a vehicle is idling, braking, coasting, or creeping forward as cars ahead move through the line.

For the test vehicles in the study, an idling engine generated 0.75 grams per second of carbon dioxide, 0.84 milligrams per second of carbon monoxide, 1.04 milligrams per second of hydrocarbons, and 1.71 milligrams per second of nitrogen oxides, a key chemical in the formation of harmful ozone.

The volume of those emissions tick up during a slow coast, when a driver takes a foot off the brake and lets the vehicle move up a few feet to an ordering speaker, payment window or pickup window. Emissions also rise with a slight acceleration to nudge the vehicle from a full stop to the next idle point or to exit the drive-through.

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Pollutants: from milligrams to tons

Milligrams and grams per second from a single vehicle creeping or idling in a drive-through lane might not seem like much. At the national average drive-through waiting time of 5 minutes 35 seconds, those miniscule amounts from a single vehicle idling represent:

• 251.25 grams of carbon dioxide.
• 281.4 milligrams of carbon monoxide.
• 348.4 milligrams of hydrocarbons.
• 572.9 milligrams of nitrogen oxides.

The milligrams and grams of invisible tailpipe emissions per second calculated by Qiao from drive-through lanes ultimately add up to thousands of tons of pollutants per year in the San Joaquin Valley.

In an interview with CVJC, Qiao noted that engine technology has improved since his research was done in 2016, but said it still represents a reasonable approximation of vehicle emissions in drive-through lanes. And it’s the incremental and cumulative effects of those emissions, concentrated near a restaurant, that are the primary health concern.

“When my (graduate) student and I discussed this project, we talked about the health issues,” Qiao said. “If you consider emissions, the total emissions from a drive-through site will be very small; however, in the drive-through area and in the restaurant, the emissions will directly hurt human health. People are very close to those emissions.”

The concentration of emissions “not only affect the drivers, it will affect the people who are eating in the restaurant (and) who are passing by the restaurant,” Qiao added. And the workers inside a restaurant – particularly those who are working at the drive-through payment and pickup windows that open and close with each customer, are also being exposed constantly to the emissions.

Tim Sheehan is the Health Care Reporting Fellow at the nonprofit Central Valley Journalism Collaborative. The fellowship is supported by a grant from the Fresno State Institute for Media and Public Trust. CVJC research assistant Marisol Herrera contributed to this report. Contact Sheehan at tim@cvlocaljournalism.org.