Will self-driving cars reduce emissions—or actually increase them?

Self-driving cars are often touted to be green. The assumption is that by eliminating congestion and driving more efficiently, they will reduce carbon emissions. That is all true. But by making driving easier and more convenient, they might make us rely on them more, negating their environmental benefits and in the worst case even increasing emissions, a new study says.

Automation by itself might not significantly affect emissions, but it would trigger many changes in the road transportation system that do have a carbon impact, according to authors of a study published in Transportation Research Part A. The net effect on emissions depends on an array of factors. “Automation might plausibly reduce road transport greenhouse gas emissions and energy use by nearly half—or nearly double them—depending on which effects come to dominate,” they write.

Carmakers and technology companies like Tesla, Volvo, Google, Apple and Uber are investing heavily in self-driving vehicles. Experts predict that driverless cars could be on urban and rural roads within the next 10–20 years.

This study by researchers at the University of Leeds in the UK, University of Washington in Seattle, and Oak Ridge National Laboratory in Tennessee is the first to assess the system-wide energy impact of automated vehicles. The team analyzed several mechanisms that could affect the energy intensity of car and truck use, depending on various levels of automation.

They found that vehicle automation may reduce the vehicle travel emissions by making driving more efficient, facilitating a shift away from individual car ownership, and altering the size, weight, and efficiency of vehicles.

Driving in tight formation to reduce aerodynamic energy consumption could result in a 4–25 percent reduction. A switch to lighter cars because of reduced crash risks could reduce energy consumption by up to 23 percent. Surprisingly, improving traffic flow and reducing congestion, often thought of as a key advantage of autonomous cars, will only cut up to 4 percent of energy use.

But several factors could increase energy use and carbon emissions, the researchers estimate. People choosing highly automated cars—in which they could work or socialize more easily—over shared transport would lead to a 5–60 percent increase in energy consumption. Self-driving cars will also allow more elderly and people with disabilities to drive, resulting in an estimated 2–10 percent increase. Higher highway speeds and demand for more equipment such as TVs in cars would also make them more energy-intensive.

“There is lots of hype around self-driving cars, much of it somewhat utopian in nature,” said Don MacKenzie, a professor of civil and environmental engineering at the University of Washington, in a press release. “But there are likely to be positives and negatives. By taking a clear-eyed view, we can design and implement policies to maximize the benefits and minimize the downsides of automated vehicles.” – Prachi Patel | 3 March 2016

Source: Wadud, Z, MacKenzie, D and Leiby, P (2016) Help or hindrance? The travel, energy and carbon impact of highly automated vehicles. Transportation Research Part A: Policy and Practice doi:10.1016/j.tra.2015.12.001

Header image via Rinspeed