Toyota introduces new 2020 Highlander and hybrid at New York International Auto Show; TNGA-K platform
UCSD researchers improve method to recycle and renew used cathodes from Li-ion batteries via eutectic molten salts

U-M study: Induced driving miles could overwhelm potential energy-saving benefits of connected, self-driving cars

The benefits of connected, self-driving cars (CAVs) will likely induce vehicle owners to drive more, and those extra miles could partially or completely offset the potential energy-saving benefits that automation may provide, according to a new University of Michigan study.

In the coming years, self-driving cars are expected to yield significant improvements in safety, traffic flow and energy efficiency. In addition, automation will allow vehicle occupants to make productive use of travel time.

1-s2.0-S0306261919305823-ga1_lrg

Connected and automated vehicle (CAV) technology is expected to be an indispensable but disruptive factor in the transportation sector, transforming the mobility paradigm, transportation markets, and travelers’ behavior in the coming decades. It will likely increase transportation safety to an unprecedented level, enhance mobility, provide a higher level of comfort and convenience for travelers, and reduce the cost of driving for individuals, all of which will be welfare-improving for society. At the same time, vehicle connectivity and automation will inevitably and significantly change energy demand in the transportation sector. The extent of these changes is still largely unclear and yet will have major consequences for energy supply and the environment alike.

Several characteristics of CAV technology will influence energy consumption, including improvements in route optimization, eco-driving, crash avoidance, and vehicle right-sizing, among others. Many of these improvements will push energy use downwards; however, some will very likely work in the opposing direction. Chief among the factors that will exert upward pressure on energy demand is the marginal cost of driving, which is expected to drop significantly with CAV technology. Higher fuel economy of CAVs will cause the per-mile fuel cost of travel to drop. This, in turn, will induce additional travel that partially offsets the fuel savings of energy efficiency—commonly referred to as a “rebound effect”. In addition, increased comfort and reduced attention requirements3 will cause the per-mile travel time cost to drop, inducing even more additional travel.

The key parameter dictating the magnitude of travel demand induced through these channels is the elasticity of travel demand with respect to the price of travel. … In this paper, we use the most recent empirical microdata available to estimate the elasticity of travel demand with respect to the marginal fuel and time costs of travel in a single, unified framework.

—Taiebat et al.

Previous studies have shown that greater fuel efficiency induces some people to travel extra miles, and those added miles can partially offset fuel savings—a behavioral change known as the rebound effect.

In addition, the ability to use in-vehicle time productively in a self-driving car—people can work, sleep, watch a movie, read a book—will likely induce even more travel.

Taken together, those two sources of added mileage could partially or completely offset the energy savings provided by autonomous vehicles, according to a team of researchers at the U-M School for Environment and Sustainability led by Dow Sustainability Doctoral Fellow Morteza Taiebat.

Conceivably, the added miles could even result in a net increase in energy consumption, a phenomenon known as backfire, according to the U-M researchers. Their study is published in the journal Applied Energy.

The core message of the paper is that the induced travel of self-driving cars presents a stiff challenge to policy goals for reductions in energy use.

—co-author Samuel Stolper, assistant professor of environment and sustainability at SEAS

Thus, much higher energy efficiency targets are required for self-driving cars.

—Ming Xu, associate professor of environment and sustainability at SEAS and associate professor of civil and environmental engineering at the College of Engineering

In the paper, Taiebat and his colleagues used economic theory and US travel survey data to model travel behavior and to forecast the effects of vehicle automation on travel decisions and energy use.

Most previous studies of the energy impact of autonomous vehicles focused exclusively on the fuel-cost component of the price of travel, likely resulting in an overestimation of the environmental benefits of the technology, according to the U-M authors.

In contrast, the study by Taiebat and colleagues looked at both fuel cost and time cost. Their approach adapts standard microeconomic modeling and statistical techniques to account for the value of time.

Traditionally, time spent driving has been viewed as a cost to the driver. But the ability to pursue other activities in an autonomous vehicle is expected to lower this “perceived travel time cost” considerably, which will likely spur additional travel.

The U-M researchers estimated that the induced travel resulting from a 38% reduction in perceived travel time cost would completely eliminate the fuel savings associated with self-driving cars.

The possibility of backfire implies the possibility of net increases in local and global air pollution, the study authors concluded.

In addition, the researchers suggest there’s an equity issue that needs to be addressed as autonomous vehicles become a reality. The study found that wealthier households are more likely than others to drive extra miles in autonomous vehicles “and thus stand to experience greater welfare gains.”

Support was provided by the Dow Sustainability Fellows Program at the University of Michigan.

Resources

  • Morteza Taiebat, Samuel Stolper, Ming Xu (2019) “Forecasting the Impact of Connected and Automated Vehicles on Energy Use: A Microeconomic Study of Induced Travel and Energy Rebound,” Applied Energy, Volume 247, Pages 297-308 doi: 10.1016/j.apenergy.2019.03.174

Comments

mahonj

I would agree with this.
I can imagine that americans would use vans with beds in them rather than cars once AV technology was proven. Then they could live 3 hours away from work rather than 2.
If you prevent them from parking in cities, they would instruct the cars to drive home or to an out of town "rest centre" for AVs and then come back in and pick them up in the evening.
So I absolutely do not think that AVs will reduce fuel use or miles driven, unless steps are taken to reduce it.
It really depends on how long it takes to get a fully autonomous (level 4 or 5) car where you could go to sleep in the car (on a highway). So it might be a while.
Shared occupancy vehicles would solve this. If you have 2 people in 1 vehicle, they can go twice as far as 2 people in 2 cars (fuelwise).

Engineer-Poet

This talk about energy consumption is ignoring the elephant in the room:  if spending even more time in a vehicle means improving quality-of-life, what are the occupants getting away from?  Some obvious candidates:

  1. Crowding.
  2. Unaffordable housing costs or poor quality housing.
  3. Crime.

Crime comes straight back to housing.  Housing without security becomes dangerous to live in, and adding security adds cost.  Crime makes some housing uninhabitable and increases demand and price for secure housing.

Crime drives energy consumption in other ways.  Mass transit is touted as "the" efficient way to travel, but in many places the buses and trains are dominated by criminal elements.  People wind up paying for transit systems that they themselves cannot use because they are too dangerous.

The only solution is to ruthlessly prosecute criminals of all kinds, and hit every accusation of "racism" with libel suits which bankrupt the accusers.  However, the trend in Baltimore, Chicago and now Boston is to go the other way, so the problem will get much worse before it gets better.

mahonj

In Ireland, it is unaffordable housing (and lack of rail transport).
Rail is the best as it is much smoother than car/bus and you can work on a laptop / read without getting queezy,
Another problem of AVs will be road congestion if everyone wants a vehicle to themselves.
Shared occupancy is the solution - the question being how many people are you most comfortable with. IMO, more is better - I am happier to be on a bus with 30 people (who I am not expected to talk to), rather than in a taxi with one (who I might or might not want to talk to), or a shared taxi with say 4-6.

dursun

you really should stay on your Meds E_P

HarveyD

One has to admit that current mass transportation (trains/buses/subways) in many large cities in USA and in most third world countries/cities, is too often unclean and unsafe?

Controlled, well equipped UBER like shared small (6 to 10 passengers) e-ADVs may be a better-safer solution, depending on membership, quality of maintenance and safety equipment operation?

Engineer-Poet

dursun, care to tell us what institution granted you your certification in psychiatry to be able to render said judgement?

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Working...
Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.

Working...

Post a comment

Your Information

(Name is required. Email address will not be displayed with the comment.)