Encouraging new evidence on eVMT.
Today’s post is co-authored with Duncan Callaway
The parking lot at our Berkeley grocery store, the one with kombucha on tap, is increasingly populated with electric vehicles (EVs). This feels like a step in the right direction. Moving people out of their gasoline-powered cars and into EVs will likely be key to reducing carbon emissions in the transportation sector.
It’s one thing to see EVs taking over the Berkeley Bowl parking lot. But what about the Mall of America?
To meet our decarbonization goals, we’ll need to convince the masses, not just the Berkeley eco-warriors, to make the EV switch. This mainstream transition is not going to happen if EVs are poor substitutes for the gas-powered cars that Americans know and love.
As Catherine and co-authors note in their blog, one way to start assessing this real-world substitutability is to ask if Americans are driving their electric cars as much as gas-powered cars. This week’s blog unpacks the latest electric-fueled vehicle miles traveled (eVMT) data from the largest EV market player…
Alternate perspectives on eVMT
Some recent studies have investigated how much Americans are driving their EVs. To put these numbers in perspective, the Federal Highway Administration estimates that US light-duty vehicles were driven, on average, 11,467 miles in 2017 and 11,599 miles in 2019:
- Lucas Davis estimates that the 436 electric vehicles in the 2017 National Household Travel Survey drove an average of 6,300 miles per year.
- Gil Tal and co-authors used data loggers to track miles driven by 358 California EV drivers. These study participants traveled 12,900 EV miles per year on average.
- Noting limitations with small and non-random samples, Catherine, Jim Bushnell, and co-authors (Burlig et al.) estimate residential EV charging using the electricity bills of PG&E customers (including over 57,000 EV and PHEV drivers!) from 2014-2017. They estimate that, on average, battery EVs travel 6,700 miles on electricity per year.
These retrospective studies are insightful. But projecting forward is complicated by the fact that the EV market landscape is changing fast. Tesla blew the doors off this market in 2018 with its Model 3, as the figure below shows. Last year, 79% of all EVs registered in the United States were Teslas.
The eVMT studies to date use data that largely pre-date this Tesla take over. This has us wondering…what’s happening to eVMT now that EVs are more sleek than science-project?
Tesla Miles Traveled
A growing number of auto manufacturers, including Tesla, are selling cars with built-in internet connections. This enables cool features like access to real-time traffic data, over-the-air software updates, and caraoke!
On-board telemetry also allows car manufacturers to capture information on vehicle usage and performance. We asked Tesla if they might share some of what they know about how their cars are being driven. They generously sent us summary statistics for daily miles driven, by model and year.
The figure below summarizes these aggregated Tesla miles traveled (TMT) data for 2019. For each reporting year, we received statistics for all Teslas delivered in the US over the previous two years, for which there were at least 30 days of data (note the sales figures above — this is a lot of cars, dominated by the Model 3). So when you’re looking at the 2019 average, that’s summarizing information for cars delivered between January 2018, and December 1, 2019.
We contrast the Tesla numbers (from 2019) with the national average VMT from FHWA and other empirical eVMT estimates. On average, the Tesla cars are driven about the same as a typical light-duty vehicle in the US, and a lot more than some prior estimates based on pre-2018 data.
Figure note: Because cars in the Tesla data were owned for fractions of a year, they provided us with daily mileage data; we multiplied by 365 days/year to make the data comparable to other reports. But it’s important to keep in mind that we’re not doing anything to correct for seasonality, or the possibly changing habits of drivers over the course of the sampling period. Empirical eVMT estimates are from the Gil Tal et al. study, Burlig et al., and Lucas Davis’s paper (all referenced above).
We’re going to go out on a limb and conclude that, when it comes to eVMT, vehicle attributes matter. Many of the EVs in earlier studies were low range (e.g. less than 100 miles per charge). The Tesla models in our data have 250-400(!) miles of range. But range may not be the only factor driving higher TMT. For example, Tesla’s extensive super-charger network could be playing a role, and its styling and acceleration may be drawing a different profile of driver.
Tesla also sent us some information on the distribution of driving patterns for their cars. We’ll save a detailed analysis for another day, but the short story is this: the median Tesla goes farther per year than the median gas-powered car. The reason the averages are comparable is that there are a few gas-powered cars that go really far per year (hundreds of thousands of miles), which lifts up the average.
On-board policy navigation?
With practically everyone jumping into the EV game (Ford, VW and Volvo recently released new models), we’re curious to know whether the driver behavior we’re seeing in the Tesla data will extend to all EVs with mainstream appeal.
Beyond our quirky curiosity, these questions are increasingly policy-relevant. The Biden administration is proposing to spend billions to help Americans make the switch to electric cars. This includes funding for EV tax credits and expanding the charging network. To effectively target and evaluate these investments, we’ll need to understand how people are purchasing and driving these cars.
Now is the time to open the conversation about how we might use these data to shape and steer policy while also respecting privacy and intellectual property. There are good examples of other market contexts in which firms share important data in the public interest (e.g. household consumption data, labor market data, mortgage market data). Our networked cars can route us out of traffic jams — can they help us chart our vehicle electrification course?
Keep up with Energy Institute blogs, research, and events on Twitter @energyathaas.
Suggested citation: Callaway, Duncan and Fowlie, Meredith. “Tesla Miles Traveled” Energy Institute Blog, UC Berkeley, June 21, 2021, https://energyathaas.wordpress.com/2021/06/21/tesla-miles-traveled/