The Fuse

Study: Quantifying the Energy Implications of Autonomous Vehicles

by Matt Piotrowski | August 29, 2016

There have been mixed views on how autonomous vehicles will shape fuel consumption patterns in the future. On the one hand, the new cars will boost efficiency, ultimately bringing about an enormous drop in fuel use. On the other, since autonomous cars will provide transportation access to a larger segment of society and will also drive at times with no one in them, vehicle miles traveled (VMT) will skyrocket and increase demand for petroleum.

An important report from the RAND Corporation lays out how self-driving cars provide a major opportunity to massively increase fuel economy and transition to alternative fuel vehicles.

As autonomous cars penetrate the country’s economy, the lighter the overall vehicle fleet will be, largely because of technological improvements and a sharp reduction in the number of traffic accidents. This shift toward lighter vehicles could ultimately help bring about a large enough increase in fuel economy to offset any potential increases in VMT. Lighter vehicles will also make alternative fuels such as electricity more cost-effective for the transportation sector, cutting demand for petroleum.

An important report from a major research group, the RAND Corporation, lays out how self-driving cars provide a major opportunity to massively increase fuel economy and transition to alternative fuel vehicles. How quickly these benefits occur depends a lot on the speed public acceptance of autonomous vehicles, the ability of lawmakers and regulators to shape policy that’s conducive to changes in transportation, and the pace of technological gains.

Massive fuel savings from lighter vehicles

Light-weighting is expected to be one of the primary drivers of efficiency gains in autonomous vehicles.

Light-weighting is expected to be one of the primary drivers of efficiency gains in autonomous vehicles. Since more power is required when a vehicle is heavier, it consumes more fuel. The graphic below shows how vehicle weight has not, on average, fallen over the years, undermining opportunities to significantly increase fuel economy.

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In terms of weight reduction, fully automated self-driving vehicles (or level 4) are likely to be pod cars that are aerodynamic, which in turn will increase efficiency. RAND points out that some experts have recommended that autonomous cars weigh just 250 pounds, compared to an average of over 3,000 pounds for vehicles currently on the road. But in order for the full fuel economy benefits to be realized, the entire fleet needs to be autonomous. One major obstacle to full-scale adoption of ultra-light cars is that consumers may balk at using them in a mixed-vehicle environment, worrying instead that their safety will be compromised if they still have to share the roads with traditional, heavier vehicles. Researchers for the RAND study note that users of alternative vehicles need “to have confidence that accidents with non-AVs are also avoided, which is likely to limit the types of substantial weight reduction to Level 3 or Level 4 automation and will depend upon nearly universal adoption of this technology so the risk from non-AVs is minimal.”

The fuel savings could be enormous, though, once the full fleet is turned over. One study that RAND quotes suggests that a networked pod fleet could see fuel economy at an astonishing 500 to 1,000 mpg for autonomous cars.

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While that outlook may be overly optimistic, efficiency is expected to take-off in coming decades, even though the improvements will happen incrementally. Recent research, such as studies from Eno Center of Transportation Research, Goldman Sachs, and others, also say autonomous cars will boost fuel efficiency sharply.

Efficiency gains will still occur even without level 4 cars, however, as the fleet is already poised to become lighter in coming years. For instance, even for vehicles that aren’t fully automated, weight is expected on average to decline by 20-25 percent by 2030 and roughly 32-50 percent two decades later. Still, roads with only autonomous vehicles provide the greater potential for a complete overhaul of how much fuel we need to use.

Autonomous cars to support alternatives to oil

In addition to (and supported by) efficiency improvements is the fact that autonomous vehicles are expected to be largely electric. One main talking point among AV advocates is that the future economy will be autonomous, shared, and plug-in. But some are skeptical of predictions that autonomous cars will be electric and see no specific reasons why the auto industry and consumers will move in that direction given the high costs of EVs and current limits with charging infrastructure. However, in order for the maximum energy security benefits to come about, the shift to EVs is vital.

The likelihood of autonomous cars being electric relies heavily on smaller and more efficient batteries.

Currently, EVs have to use batteries that are expensive and heavy. If these two factors change for the better, and they likely will given the continuous improvements seen in battery technology, then the robot cars you’ll see on the street will mostly run on electricity. The battery in the Nissan Leaf weighs a massive 600 pounds and costs $10,000, factors that add to the vehicle MSRP and turn off some potential consumers. With the expected weight reduction for cars, alternative vehicles could use smaller batteries that cost less without compromising range. The lower costs would make EVs more attractive for any consumer with trepidation. “If Level 4 automation enables ultralight, pod-like AVs, these would require far smaller batteries to travel the same distance as a conventionally sized vehicle,” RAND said. Once the battery size decreases, there’s more potential for autonomous cars, and even conventional ones, to run on electricity. Consumers won’t be turned off by high battery costs and they can save even more over the life of the vehicle since they won’t have to fill up at a gas station. “If automation Levels 2, 3, and 4 enabled the expected weight reductions, AVs fully or partially powered by electricity would be able to travel the same range using batteries that are smaller, and thus cheaper.”

“If Level 4 automation enables ultralight, pod-like AVs, these would require far smaller batteries to travel the same distance as a conventionally sized vehicle.”

Batteries could also be charged more often, which would also allow for reduced battery size. Cars could drop their occupants at their destination and then head to the nearest station to recharge. Further out in the future, cars could use inductive wireless charging, which transfers energy from one object to another. Against this backdrop, level four autonomous cars would be disruptive for the petroleum sector.

But as long as the internal combustion engine stays with us, the dependency on oil will continue. If autonomous cars aren’t overwhelmingly EVs, the shift to autonomy could bring about some worrisome trends given that they could increase VMT. With the cost of driving declining and traveling becoming more comfortable with autonomous cars, more people will be willing to drive further. At the same time, higher VMT will also likely result from the fact that autonomous cars are poised to open opportunities to segments of society who didn’t have their own vehicles before. Ride-sharing services, meanwhile, could lessen the use of public transportation. All of these factors complicate the shift to autonomy.

Over time, what’s important is that the gains in fuel economy offset the very likely increase in VMT that comes from greater cost savings for the consumers prompting them to drive more.

Over time, what’s important is that the gains in fuel economy offset the very likely increase in VMT that comes from greater cost savings for the consumers prompting them to drive more. RAND points out that a car with fuel economy 31 mpg would consume about 400 gallons of gasoline traveling 12,370 miles throughout the year. If VMT increased to 20,000 miles per year, a car with that gets 50 mpg would consume the same amount of gasoline.

Social benefits apparent

RAND’s study encompasses a wide variety of issues intended to educate policy makers about autonomous technology, safety, regulation, cybersecurity, and liability. “Careful policymaking will be necessary to maximize the social benefits that this technology will enable, while minimizing the disadvantages,” the study says. The risks and uncertainties surrounding autonomous vehicles are well known, but their potential to disrupt the petroleum sector through greater fuel economy and hastening a full transitions to EVs is becoming more apparent.

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