How much do drivers use EVs? Clashing studies fuel debate

By Anne C. Mulkern | 02/19/2021 07:29 AM EST

A study on California electric vehicle usage is firing debate on an urgent question for policymakers: How much are EVs driven compared with gas-fueled cars?

 A recent study published by the National Bureau of Economic Research is raising questions about how far electric vehicles are driven relative to gasoline-powered cars.

A recent study published by the National Bureau of Economic Research is raising questions about how far electric vehicles are driven relative to gasoline-powered cars. Claudine Hellmuth/E&E News (illustration); boboroshi/Wikipedia (sign); S. Hermann & F. Richter/Pixabay (highway photo); NeedPix (car drawing); Franz Blees/Wikipedia (car diagrams); Internet Archive Book Images/Flickr (drafting elements)

A study on California electric vehicle usage is firing debate on an urgent question for policymakers: How much are EVs driven compared with gas-fueled cars?

There’s still no clear answer even as California, the Biden administration and some major automakers look to a massive shift to clean cars.

The study last week by the National Bureau of Economic Research said that as of 2017, EVs on California roads traveled less than half the distance driven by an average gas-powered vehicle (Energywire, Feb. 8).


But some Golden State academics and state officials pounced on the analysis as faulty, citing their own reviews of the hot-button issue.

"This research is flawed from beginning to end," said Gil Tal, director of the Plug-in Hybrid & Electric Vehicle Research Center at the University of California, Davis. Its conclusions went "about five bridges too far," he said.

Tal and a team at the EV Research Center analyzed the topic for the California Air Resources Board (CARB) last year and plan to issue an updated research brief in the coming weeks.

Criticisms of the NBER study prompted its researchers to post a response yesterday, defending points they made.

"We were surprised by our findings as well, and have taken a number of steps to stress-test them," they said in a blog post.

The NBER study analyzed how much electricity EV buyers used in the 25 weeks before and after their auto purchase. It calculated charging levels using utility bills in the San Francisco region and factored in data from public charging stations.

The study said its findings raise "questions about (among other things) the true extent of EV usage at present, how EVs fit into the residential transportation portfolio, and the role of gasoline and electricity prices on EV usage."

It comes as President Biden and California Gov. Gavin Newsom (D) push for far more EVs and charging infrastructure. That will require spending that’s likely to face political pushback, especially if critics can point to evidence the cars aren’t as useful as gas cars for long-haul trips.

California is the national leader in EV adoption, home to half of all the EVs in the country. Newsom last year told CARB, the state’s influential emissions regulator, to pass regulations banning sales of new gas-fueled cars after 2035.

"Electric vehicles are clearly the most important strategy for reducing emissions from the transportation sector, which is turning out to be the most difficult sector to crack," said Dan Sperling, member of CARB and founding director of the Institute of Transportation Studies at UC Davis. "It is important, therefore, that EVs not get politicized, not become a partisan issue. Researchers that suggest that EVs are inferior are lending themselves to that narrative."

Critics called the NBER analysis outdated, as it looked at EV driving between 2014 and 2017, when "most [battery electric vehicles] had a shorter range than those on the road today," Lindsay Buckley, California Energy Commission spokeswoman, said in an email.

In 2014, 73% of battery electrics had a range of less than 200 miles per charge, California data shows. By 2017, the number of cars constrained to that range had dropped to just over half, Buckley said.

The Tesla Model 3, when it came out in 2017, could last up to 310 miles on a charge. By 2019 in California, 76% of all-electric plugs-ins could go more than 200 miles on a charge.

The NBER researchers’ "sample does not represent electric cars in California, and for sure does not represent the future cars in California," Tal said.

The blog post yesterday said that "there are reasons to believe that people who bought EVs over the last 3 years may drive them more than people who bought EVs from 2014-2017."

"But, we do not see any detectable changes in our results from 2014 to 2017, and some of the same factors were at play over this time period," the post said. "This makes us think that newer data might not be dramatically different, but we don’t know."

The study looked at battery electric vehicles as well as plug-in hybrid cars, which use both electricity and gas. But it only accounted for the electric miles of those cars, Tal said, which doesn’t fully reflect how much they were used. And it failed to account for charging at drivers’ workplaces, he said. Workplace charging for many drivers is free, so they use that option, he said.

Dave Rapson, a UC Davis researcher involved in the NBER study, said the amount of unmetered workplace charging is unknown, "but it’s likely small because workplaces that aren’t metering are leaving money on the table" by forgoing a California credit for those providing non-gas-fueling options.

"However, even if the workplace channel comprises 10% of commercial charging, that would lead us to adjust our annual [electric vehicle miles traveled] estimate from 5,300 to 5,435. It doesn’t really move the dial," he said in an email.

The NBER study acknowledged the limits of its findings, said Fiona Burlig, energy and environmental policy professor at the University of Chicago and a fellow researcher on it.

"It’s definitely correct that we’re using a relatively early sample of EVs," Burlig said in an interview. "The fleet in 2017 is not the same as the fleet in 2021. … I’m not trying to say that we are predicting the future, but I do think it’s important to understand what EV driving has looked like."

Multiple answers

In their own paper last year for UC Davis, Tal and two other researchers detailed four estimates for miles traveled by EVs in California: one from the 2017 National Household Travel Survey (NHTS), a database for travel behavior studies; another from the California Energy Commission’s California Vehicle Survey in 2019; a third from a 2019 UC Davis survey; and one from data collected by vehicle loggers installed as part of ongoing UC Davis research.

Those tallies differed substantially, the UC Davis study said, in part because of the wide range of years they covered and the various electric models available in those time periods.

The UC Davis paper split battery electric vehicles into short-range and long-range categories. Researchers noted that short-range models included in the 2017 NHTS study "are mostly not sold anymore and have been replaced by longer range versions."

For long-range EVs, annual miles driven ranged from 9,300 in the NHTS report to nearly 15,000 in the more recent logger data. That compared with gas cars’ average travel of between 9,010 miles and 10,790 miles per year.

The California Energy Commission gathered data for its 2019 survey by asking motorists to self-report their annual miles driven, said Buckley with that agency.

Owners of both battery electric vehicles and plug-in hybrid EVs drove a median 10,000 miles annually, Buckley said. Plug-in hybrid owners reported that 5,250 of their 10,000 annual miles were electric.

"By contrast, internal combustion engine (ICE) vehicle owners reported their median number of miles was 8,000," Buckley said.

Tal and the other UC Davis researchers in their paper said it showed the importance of developing a better method for tracking the miles traveled by plug-in EVs.

"All things considered, [a] credible estimate of [plug-in] usage is required to guide policy related to transportation electrification," the study said. "The varying estimates … demonstrate the need for rich data that can track the changes in vehicle technology as well as the demographics of [plug-in] adopters."

This story also appears in Climatewire.