How Driverless Cars Could Lead to More Pollution

Self-driving cars are still a few years away (at least) from being available to you or me. But there’s a lot of work to do to get them ready for prime time, including ensuring they’re climate-friendly. A new study underscores that last part, showing that nearly one-third of people would choose an autonomous vehicle as a regular transportation option—and that could make emissions go up as demand for these kinds of cars rises.

“We saw that there’s a lot of interest out here, and this interest might be masking some potential impacts,” said Wissam Kontar, a PhD candidate at the University of Wisconsin-Madison and the lead author of the study, published last week in Environmental Research Letters.

To get a handle on how driverless cars might change our energy system, Kontar and his team first wanted to gauge how much people would prefer to take them over other options. The researchers designed a survey that asked respondents their preferences for getting around town based on four different choices: a privately owned car, an autonomous vehicle taxi operating like Uber and Lyft, a bus, and a bike. They then polled the preferences of more than 600 people living in Madison, Wisconsin, a city with what Kontar describes as a robust bus system (in a population of just under 260,000, nearly 55,000 people rode the bus each weekday before the pandemic) and a bike-riding culture in the summers.

I know that I don’t have an automatic, blanket preference for how I get around; among other things, I factor in the length of the trip, the distance of walking to a subway stop, and what the weather’s like. Researchers also designed the survey to reflect those types of considerations. In the survey, participants were shown examples of different trips within Madison and given all sorts of information with each transit option, including waiting time, cost, walking time to a pickup point or bus station, and parking ease.

For me, Uber and Lyfts usually score pretty high on my “convenience” scale, but there’s a real downside to the cost; I’d imagine a lot of people also pause at paying $25 for a car ride that could be a $2.25 bus fare with just a little bit more time and walking involved. But there is a key difference between what future autonomous vehicle service could look like and current ridesharing options: the cost of labor. Without a human driver in the seat, economists say, autonomous vehicles could be a lot cheaper than hailing a taxi or an Uber today. (This, of course, is great news for riders, but pretty disastrous for the thousands of people who now depend on ridesharing as a career.) Kontar said the study incorporated this potential lower cost into the analysis, which gives autonomous vehicles “an edge” compared to present-day taxis and rideshare cars.

When all was said and done, the overall findings were pretty good for autonomous vehicles. In the scenarios, the majority of choices were split between using a personal vehicle (32%) and an autonomous one (31%). Bikes won about 21% of the time, while buses scored a measly 16%.

This, Kontar and his team found, could mean dirtier air and more greenhouse gas emissions for Madison. More gas-powered autonomous vehicles on the road and fewer riders in buses, the study found, could boost energy use from transportation in the city by almost 6%, as public transit use decreases; this would correlate with a 5.7% rise in greenhouse gases. Meanwhile, emissions of harmful particulate matter, sulfur, and nitrogen oxide from more cars on the road could also all increase between around 6% and 7%.

The easy solution here, it seems, would be to ensure that all self-driving cars put on Madison’s roads be electric. But Kontar and his team also caution that vehicle electrification needs to come with sweeping reform of our electricity system. Wisconsin, the study notes, still generates more than 40% of its electricity from coal. While electrifying autonomous vehicles would help reduce emissions from more cars on the road and harmful particulate matter tied to them, loading up a fossil-fuel-powered electric grid like Wisconsin’s with more demand could have adverse impacts.

“If you’re generating the electricity from coal versus generating electricity from wind, these have completely different environmental impacts,” Kontar said.

This survey and the study was, by design, pretty specific to Madison. The popularity of autonomous vehicles and emissions tied to them could vary based on other options available to folks in other cities. But it does seem pretty clear that a cheap, fast driverless car that takes you from door-to-door would be an alluring option for most people, particularly in other cities with less biking, walking, or public transit infrastructure. Now is the time to start thinking about what that option may mean for the planet in the long run.