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All Charged Up, No Place to Go

Today EVs are driven much less than other cars, which has big implications for the environment.

Where in the country you drive an electric vehicle matters a lot for the environment, a point made repeatedly — both by economists (here and here) and by engineers (here and here).

You know what else matters a lot? How much you drive. This gets very little attention, but has major implications for the environmental impact of EVs.

After all, it isn’t the manufacturing of EVs that gives them their environmental edge. If anything, the copper, aluminum, and lithium required to build batteries actually make EVs somewhat more resource intensive.

Instead, the prospect for EVs as a climate change solution hinges on their ability to reduce gasoline consumption. But how much gasoline is actually saved depends, crucially, on how many miles the EV is driven and on how many miles the driver would have otherwise driven in a gasoline vehicle.

How Much Are EVs Actually Driven?

Although this seems like a straightforward question, there is surprisingly little direct evidence.  Last year in our blog, Jim Bushnell lamented that we know little about how much EVs are driven.

To shed light on this, I constructed the figure below using newly available nationally representative data from the 2017 National Household Travel Survey (NHTS).  Prior to the 2017 NHTS, the most recent NHTS was conducted way back in 2009, when there were virtually no EVs on the road.

A valuable feature of the NHTS is that respondents fill out an “Odometer Mileage Record Form.”  I took these odometer readings and divided by the age of each vehicle to calculate the average number of miles driven per year. The table below plots averages for four different types of vehicles.

fig1

Thus according to these data, EVs are driven significantly less than other types of vehicles. All-electric and plug-in hybrid vehicles are driven 6,300 and 7,800 miles annually, respectively, compared to 10,200 for gasoline and diesel vehicles, and 12,000 for conventional hybrids.

I find this pretty surprising. After all, the basic tradeoff with EVs is that they cost more to purchase than gasoline vehicles, but cost less to operate per mile. So EVs are an investment that pays off the more you drive, and consumer guides tend to recommend EVs to commuters and other people who drive a lot. I expected the opposite pattern, with EVs tending to be driven more than other vehicles.

What is Going on?

The most obvious explanation is limited range. The first generation Nissan Leaf, for example, has a range of less than 80 miles, making it impractical for roadtrips. This limited range impacts who buys EVs, and also impacts how they are used. For example, many households that own EVs have more than one vehicle, so they may just decide to leave the EV at home on high-mileage days.

Note: Today’s Nissan Leaf S has a 30kwh battery, and a 100+ mile range.   Image licensed under creative commons. https://www.flickr.com/photos/pittou2/

It is not clear how much limited range should matter for plug-in hybrids. With a plug-in hybrid you always have the option to run on gasoline, so they are not subject to the same range limitations as all-electric vehicles. Still, many plug-in hybrid vehicle drivers purchased their vehicles with the intention to use them primarily powered by electricity, so this may still have a big impact on the type of driver who buys these vehicles.

Most other potential explanations are variations on the type of person who buys an EV. For example, it could be that urban vs rural can help explain the pattern. Urban households may be more likely to buy electric vehicles, perhaps because of stronger “green” preferences in urban areas, and may also tend to drive fewer miles per year. Previous research has shown that environmental ideology is a major determinant of what kind of vehicle people buy, so the mileage pattern may simply reflect the characteristics of the places where EV buyers tend to live.

So What?

Regardless of the explanation, this pattern has important implications for the environment. In particular, it suggests that so far EVs imply far smaller gasoline savings than previously believed.

For example, a recent study called “Are There Environmental Benefits from Driving Electric Vehicles?” by Energy Institute alumni Erin Mansur and coauthors, finds that the environmental benefits from replacing a gasoline vehicle with an EV in California are worth about $2,800. Reading the fine print, however, Mansur and coauthors make this calculation assuming that all vehicles are driven 15,000 miles per year. If, instead, each EV is avoiding only 7,500 miles per year driven in a gasoline vehicle, then the benefits are half as large, only $1,400.

I’m not trying to pick on Mansur and coauthors. Other analyses on the use of EVs also rely on what seem to be overly optimistic assumptions on miles driven. Another well-known model in this space is the “GREET” model”, which assumes that EV batteries are used for a lifetime of 160,000 miles.  Moreover, federal CAFE standards use a lifetime for cars and trucks of 195,000 and 225,000 miles, respectively. All these measures seem high relative to the newly-available evidence from NHTS. For example, dividing 195,000 by 7,500 mile per year, implies an implausibly long average lifetime of 26 years.

The broader point is that mileage matters for EV policy. What we ultimately care about is reducing gasoline consumption, but current policies like the $7,500 federal tax credit treat low-mileage and high-mileage drivers uniformly. Is there some better policy that would target EVs to high-mileage drivers?  Why, yes, there is. It is called a gasoline tax. Making gasoline more expensive would incentivize EVs for all drivers, but the biggest incentive would be for people who drive a lot of miles.

roadtrip
Note: No long road trips for EVs? Image licensed under creative commons. https://www.flickr.com/photos/daxis/

 

For more details see Energy Institute Working Paper, “How Much Are Electric Vehicles Driven?

 Keep up with Energy Institute blogs, research, and events on Twitter @energyathaas.

Lucas Davis View All

Lucas Davis is the Jeffrey A. Jacobs Distinguished Professor in Business and Technology at the Haas School of Business at the University of California, Berkeley. He is Faculty Director of the Energy Institute at Haas, a coeditor at the American Economic Journal: Economic Policy, and a Faculty Research Fellow at the National Bureau of Economic Research. He received a BA from Amherst College and a PhD in Economics from the University of Wisconsin. Prior to joining Haas in 2009, he was an assistant professor of Economics at the University of Michigan. His research focuses on energy and environmental markets, and in particular, on electricity and natural gas regulation, pricing in competitive and non-competitive markets, and the economic and business impacts of environmental policy.

17 thoughts on “All Charged Up, No Place to Go Leave a comment

  1. All research in the EV industry will have a substantial impact in how electricity is generated and distributed, because it will free supply driven technologies like solar or wind to be available according to demand. Thanks to the EV industry we are making progress in the energy storage technology, so needed in developing countries, where off the grid solutions to electricity access are limited because of the limited use of solar or wind.

  2. As Jim Lazar suggested, people who can afford to buy new EVs might also be able to afford to live a reasonable distance from their workplaces and not have long commuted. Also, my motivation to drive an EV is the same live-lightly attitude that makes me want to minimize my driving and use public transportation when I can.

  3. Echoing Prof. Sklar’s comment, I think the profile of owners of EVs is transforming. Early adopters were likely using them for around-town, and using their larger ICE vehicles for longer trips. With the EV and PEV product development of late, more and more consumers can rely on them as the first or only family vehicle, and that should change the share of VMT these vehicles will see. Adding more plug-in SUVs will transform this too.

    My family’s new (first) PEV is our primary vehicle, gets 90% of our family mileage (in spite of our 15k annual lease mileage cap, which we will surely blow through), so that our now aged-but-beloved ICE vehicle can limp along for more years at lower mileage, for those increasingly rare instances when a second vehicle is needed. Were we a wealthier family (matching the specs of the earlier adopters) I imagine our story might be different.

  4. Lucas, I follow all of your reasons why EV drivers drive less. Here’s another possibility: do EV drivers use their cars less because, having made such a significant switch away from gas-powered cars, they are more tuned-in to conservation and efficiency as a way of life? Once people begin recycling at work, they are likely to recycle more at home and when they’re traveling. Once you start composting food scraps, it’s hard to go back to dumping them in the trash. Et cetera.
    What do you think? Sarah

    Sarah Finnie Robinson
    The 51 Percent Project
    Senior Fellow, Institute for Sustainable Energy, Boston University

  5. My wife and I bought a Chev Bolt in August. We take turns driving the Bolt based on who will be driving more on a given day. The person driving more will drive the Bolt. We intended to use the Bolt as a vehicle for everyday use but not for long trips. When we make 4 hour or longer trips we take our gasoline powered vehicles so we do not have to charge away from home. The key to us has been the great range on a single charge. We treat the Bolt the way we treat our phones. We plug it in at night, at home, and when we wake up it is fully charged. With a 200 mile plus range and mostly in town driving, we would have to drive for 5 or 6 hours a day to need to recharge. That is just never going to happen in our driving patterns. So, my thoughts about less driving are all about the range.

  6. Many EVs are leased so they will never be driven over 12K miles a year. EV owners tend to be more affluent and have shorter commutes and many can work from home. A lot of research by Brookings and others has demonstrated that commutes increase as the income level decreases. As income gaps increase so do the average commute differences. This accounts for about 15 to 25 % of the mileage differences.

    I sure do like my Nissan LEAF, best commuter car we have ever owned. It was worth waiting for 18 months to get it back in 2011. Much better commuters than our Prius’s, Camrys, Corrollas, Miata, or CRV. Much much better than my old 300Zxs, Datsuns, Infinitis, Land Cruisers and SR5s. Great cars. If you can use an EV in the 20-80% charge range and save 100% for trips out of town they will easily last 2x to 4x the battery warranty period.

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