The emobility research team at the Chemnitz University of Technology. The "Cognitive and Engineering Psychology" group is headed by Prof. Dr. Josef F. Krems.

How far does an electric car go on a charge? The answer is determined more by perception than the vehicle’s battery capacity, according to a new study by a team of German researchers. In a paper to be published next month, “Experiencing Range in an Electric Vehicle: Understanding Psychological Barriers,” the team of psychologists from Chemnitz University of Technology reports on a six-month field study with 40 drivers of the MINI E all-electric car.

“As far as I know this paper is one of the first that aims at a systematic understanding of the psychology of range experience, including stress-related personality traits, coping skills, and the ability to deal with ambiguous range,” said Thomas Franke, the paper’s lead author.

Drivers based in Berlin were interviewed prior to starting to drive the EV, again after three months of driving, and then after six months. I spoke with Franke about the research and its implications for adoption of electric vehicles.

Check out this excerpt from our discussion. Submit your questions for Franke in the comments below, and I’ll do my best to get him to respond.

Brad Berman: In your paper, you introduce the idea of “comfortable range,” as perhaps more important than the technical range. Please explain “comfortable range.”

Thomas Franke: Each user has a certain comfort zone when dealing with range. How close does the car get to empty before you usually recharge? If someone buys an EV that promises 100 miles, and spends a certain relatively high price, you wouldn’t think that 20 percent of the range capacity would go unused. But this is exactly what happens.

From our field study data on how users deal with and experience range, we have derived the rough estimation that users will only utilize about 80 percent of their available range—meaning the range that is displayed when the car is fully charged.

We have termed the variable behind this phenomenon as "comfortable range," meaning the share of the range resources that a user is comfortable to utilize. In other words, it’s the longest trip distance or the lowest level of charge still experienced as comfortable.

Do you believe that range is ultimately subjective, determined by the driver’s level of tolerance to uncertainty?

Available range can also be defined objectively with standard driving cycles, just like with internal combustion vehicles. Yet, there are many influencing factors. Each user will get a different range figure displayed on a daily basis. We call this performant range—a distance determined, for example, by whether or not he frequently likes to enjoy the sporty driving experience of his EV. Other users are interested in maximizing range, and develop an understanding of the dynamics of depleting and recharging a battery. We call this range level competent range.

The knowledge of what you can achieve on a daily basis and as a maximum value is your baseline. From there, you can modify your driving and trip-taking based on your willingness to deal with uncertain, potentially stressful, and demanding situations.

So, yes, I believe that range is heavily dependent on the subject behind the wheel and in front of the plug. This becomes visible in the sizeable variation in comfortable range values that we observed.

What are some of the ways that electric car drivers respond to the uncertainty? Here, I’m thinking of your concept of “stress-buffers.”

The experience of stressful range situations—often called range anxiety in its most extreme form—was not common among the EV drivers in our field study. Instead, we found that users simply avoided uncomfortable range situations by limiting their trips or topping up their batteries even when it wasn’t necessary.

How often did electric car drivers choose not to make a trip because of range limitations?

Users estimated that they could do 93 percent of their usual trips with the EV—if discounting problems with limited cargo/passenger space in the MINI E. We are currently working on combining data from one-week travel diaries of nearly 100 EV users to get a more precise picture of trips where the range of the EV was subjectively perceived as a usage-barrier.

How important was it that Berlin has 50 public EV chargers? Would the results be much different for a non-urban environment, or one without public charging opportunities?

From our experience, these public chargers really have some psychological value. Although nearly half of the users never used a charging station and nearly 90 percent of the users only used public chargers between 0 and 10 times within the 6 months—two-thirds of the users still considered it as essential to have them in an electric mobility system. So it might be that comfortable range would even have been lower in the study without these public chargers.

Concerning urban versus non-urban, of course, users would tell you that it is especially unpleasant if you are somewhere on a country road during the night with a low battery, but on the other hand, traffic conditions might be more predictable if you drive in a non-urban environment. This is worth further study.

How did drivers adapt their behavior or change their attitude over six months of driving an electric car?

People liked driving an electric car in the beginning, and by the end, they liked it even more. That is the very basic finding that we repeatedly obtained in three subsequent field studies where users had the chance to gain experience over several months. My colleague Franziska Bühler has published more about the dynamics of growing acceptance over time.

And my colleague Peter Cocron published a conference paper this year where he contrasted expectations and experiences concerning the low noise level issues. Before driving the EV, drivers reported that they expected substantial problems due to the lack of noise. But over time, drivers get a more balanced view concerning the risk associated with low noise as they experience very few critical incidents.

For range, one area for further analysis will be to look more closely at the learning process of adapting to certain range levels over time.

In the end, only 7 out of your 36 users said they were not satisfied with range, and on average users reported just one single range-related stressful situation per month. So, is range really a minor problem only for a small subset of drivers?

Indeed, this is perhaps the most important message of the paper: Electric mobility works in its present stage of development. Users could integrate an electric vehicle in their mobile lifestyle. Ninety percent of the users agreed that the range offered by the EV was sufficient for everyday use.

But there are real price issues when it comes to building and selling electric cars with various amounts of driving range, so every kilowatt-hour counts. So the issue of range cannot yet be dismissed. The mission of the paper is to broaden the focus in research activities from solely improving battery performance to possibly more cost-effective and tailor-made psychological interventions, such as improving users' awareness and understanding of range.

For more information, see the project website for the research.