The Planet is Begging Us to Drive Less

Climate disasters are mounting across the Golden State. While wildfires are currently raging from north to south, our neighbors are also contending with worsening heat waves and floods — and unless we act urgently, things will only get hotter in years to come.

According to numerous assessments by climate researchers, climate action will require that we reduce the number of miles we drive significantly — at least 30%, by some measures. The UN’s Intergovernmental Panel on Climate Change (IPCC) estimates that we will need to reach net zero global CO2 emissions by 2050 to prevent an average temperature increase of 1.5 degrees Celcius.

But transportation infrastructure lasts a long time. A freeway expansion, or gas-guzzling SUV purchased today, will continue to pollute for decades. A new paper by Alarfaj et al (2020) from Carnegie Mellon University explains why drastic reductions in car travel have to be a part of the solution.

Key takeaways:

1. While there has been progress in decarbonizing electricity, global emissions from transportation are growing.
2. In order to meet our emissions reduction goals, we would need a market penetration of Electric Vehicles (EVs) at a rate of 67-84%, and a near-total decarbonization of electricity.
3. Currently, EVs make up just 0.43% of cars on the road. We’re not going to meet our emission reduction goals without major policy interventions to reduce demand for cars, while at the same time decarbonizing electricity and ramping up EV adoption.

Do these takeaways sound familiar? In 2018, the California Air Resources Board (CARB) came to the same conclusion: the board’s Progress Report concluded that California must reduce Vehicle Miles Traveled by 25% to reach its emission reduction goals by 2040. The report recommended planning for more density near transit and walkable neighborhoods so that more Californians could enjoy a car-free commute. Alarfaj et al join the chorus of scholars reminding us that this needs to be a global shift in behavior.

Under current projections, a “business as usual” scenario would just slightly nudge emissions down below today’s rate by 2050, thanks to increases in fuel efficiency. But with transportation representing 33% of all US CO2 emissions, we can’t afford to wait. Because of all this uncertainty, Alarfaj et al note that “potential modal shifts away from personal vehicles to public and active transport should be one of the strategies for transport GHG reduction.”

The researchers modeled the likely scenarios that would bring us to an 80% or 90% GHG emissions reduction in transportation from 2005 levels. There is some good news to be found in the methodology, including how the models account for increased fuel efficiency. Moreover, “US electricity carbon intensity (CI) has decreased by about 30% since 2001 and is expected to further decrease with a continued shift from coal to natural gas and increased renewables.”

The results are initially quite straightforward: “We find that reducing [personal vehicle] CO2 emissions to 250 million metric tons is attainable if the electricity carbon intensity is reduced to zero and about 67% of [personal vehicle] travel is electrified,” the authors report. “For the 90% reduction target, about 84% travel electrification would be needed.”

But that’s not all. “Assuming no travel demand reduction, there is only a narrow region of EV miles and electricity carbon intensity combinations that can meet the climate target,” Alarfaj et al report. In other words, given the high uncertainty surrounding electricity decarbonization and EV adoption, there’s little room for error. If either of these variables falters even a little bit, the total “travel budget,” meaning the limit of Vehicle Miles Traveled (VMT), gets tighter. The modeling finds that reducing the total volume of car trips makes it far more likely that we can meet 2050 targets.

“If VMT is reduced through mode shifting and advanced mobility approaches, the possibility frontier of meeting the carbon reduction target expands, and fewer EV miles are required,” they argue. “However, the opposite would occur if advanced mobility technologies result in increased total VMT. For example, reducing VMT to 2 trillion miles in 2050 would require a minimum of 45% EV travel, while increasing VMT to 4 trillion miles results in [a] minimum of 73% EV travel to meet the 80% target”–so why push our luck?

Here, as a cherry on top, is the doozy of a chart that lays out the numbers. The blue line represents the EV adoption rate we would need to meet our climate goals with a reduction in car trips equivalent to no driving in the 10 densest cities in the United States: